First time poster here. I've been in some FB groups, but a lot of them are very negative and I'm hoping I'll get a more rounded answer base here for some perspective. 

Okay, so here goes. SO and I have been together about a year and a half, and we are the full-time caregivers for his two youngest children, SD3 and SD4. They live with us, BM voluntarily gave up custody but she does like to see them on a somewhat-regular basis. We try to make this work the best we can because as far as we've ever seen she treats the girls well, enjoys spending (limited amounts of) time with them, and wants to be part of their lives. The only complaint we usually have is that she we go through bad stretches where she'll just drop off the face of the earth for weeks or months, and of course this upsets the girls quite badly.

However, even though she's been coming around at the moment she's still in a bad place right now. She's dating an abuser, so the kids are not allowed to meet/be around/go over to their house. She generally either spends time with the kids at the home of one of her relatives (that we thoroughly trust), or she comes to see them at our home (sometimes I'm there, sometimes it's just SO, but I have no trust issues w/SO so this has never bothered me). We've made all our decisions regarding this together after discussion about what is best for the girls, and what we are both comfortable with on an individual and couple basis. In the past we have tried to help her out of her bad situation by encouraging her to leave, helping provide food when she was between jobs and barely eating, and occasionally loaning her small amounts of money when she was coming to visit the girls for gas, or medicine. Nothing monetarily huge since we're pretty tight on money ourselves, but we were willing to help in small ways as long as she was demonstrating a willingness to engage with the girls, it was for valid reasons, and it wasn't anything financially significant that we couldn't afford to part with.

Well, we just discovered that BM has been caught stealing a large quantity of money from aforementioned trusted relative over a period of time, and is no longer welcome in their home. A serious drug problem is very strongly suspected. If this had just been between her and aforementioned relative, and didn't involve us or her visits with the girls we could probably overlook it, let it go, and let the visits continue for the girls' sake. However, I have been searching for my laptop for the last month and haven't been able to find it. Our house is sometimes a bit on the messy side (we do our best, but it's hard to keep up with the little ones/jobs/etc), and I hadn't even thought about it until this relative mentioned the situation. However, we're now highly suspicious that she might have walked out with it one day, hoping to sell it for money (it's a Macbook Pro, so even though it's a couple years old and password-protected she might've thought she could get something out of it). Not only that, but back in December my keys went missing to my car. Long story short, it turned out to be SD4 (as we'd always suspected) hiding them so that Daddy wouldn't have to "go to work", but she put them back in my purse a few weeks later. Shortly after that my wallet went missing, and we thought the two correlated. We have, however, been searching for my wallet now since January, and my laptop for the last month. While we haven't had a chance to literally turn EVERY INCH of the house upside down, we've looked in all the obvious/unobvious/somewhat obscure places and still haven't located either one. We thought the wallet was SD4 for the longest time, but it's much larger than the keys and she promises she didn't take it, and I don't feel like she would've held onto it for this long.

So now, of course, the dilemma is that we have two things missing. We have no PROOF that BM took the items, but it seems like a strong possibility. We *do* have knowledge that she's been stealing from one of her OWN relatives, and that it's not just nickels and dimes. We've heard stories that lead us to suspect a drug issue, but we have no evidence. Both items went missing around the time BM was visiting the girls at our house. Obviously, we don't really WANT to let her back in the house, but at the same time we're concerned about the well-being of the girls. We don't want to trash-talk their Mom (we always try to keep conversations about why Mommy can't live with us/come by/be at relative's house) with age-appropriate answers that don't cast her in a bad light. We're not trying to badmouth anyone, that's not what kids need to hear. We tell them that she loves them, we support their love for her. We don't lie about it - we've explained depression in an age-appropriate manner, and explained that sometimes Mommy is sick in a way that makes her sad and tired and makes her not want to or able to do some of the things she'd normally do, that sort of thing. When they get older they can make their own decisions, but we don't believe in talking down about their mother in front of them.

So, what would you do? If we let her back in the house, no matter how well we try to supervise her now it's hard to never take your eyes off someone. I don't want to let someone I don't trust into the house, who knows if she'll try to pocket some movies or a Nintendo DS, or some other nonsense. She can't take the girls to her home, or to her relative's home anymore. She's emailing SO, asking if she can come over and see the girls, and we just don't know what to do. If it gets brought up to her, I imagine she'll deny everything, get mad, and drop off the face of the planet again. It seems almost inevitable that it'll get brought up at some point too, whether it's cause she notices someone's always in the room with her, because she senses a bit more hostility now, or because we don't want her to stay for as long anymore. While it would certainly be easier on us for her to just never show up, it's still so hard on the girls to never see her. And when they ask why, what do we tell them? I don't like to lie to them. They're clever, and quick, and can usually pick up when someone is hedging around the truth. They ask very probing questions, and I don't want it to ever seem like we're trying to turn them against her either. We also, as they get older, want them to know that we're their safe space - the people they can TRUST - so we try very hard not to lie or break promises. I've heard so many stories about how badly that can backfire. Of course, I also don't love the idea of the girls seeing her do something not okay and picking up on those kind of behaviour patterns as they get older, either. 

The whole thing is a big mess, and to top it off I'm personally quite furious at her because not only did I have information I won't be able to retrieve on that MacBook (and no, before you asked, I never got around to registering it with "Find my iPhone" because I'm busy, and an idiot, and now I'm kicking myself really hard for it), but I'm also just TICKED. She couldn't have asked for a better stepmom. I've been kind, courteous, I try to give her the benefit of the doubt, I supported SO's choice to help her out when she didn't have food, I send her occasional pictures of the girls, I've offered to drop them off if it's convenient for visits, I've NEVER been rude to her, I tried my hardest to be a good co-parent. And while the whole thing seemed a little awkward for her at times, for the most part we got along fine. Now, if she did steal from me, she's made all our lives a whole HECK of a lot more inconvenient and frustrating. I just don't know what to do, and neither does SO. We want to do what's right for the girls, but we don't want to set ourselves up to get taken advantage of again either.

To top it off, even though they've been apart for several years now there were some paperwork and money issues after their split and the divorce was never finalized. We still need to do that (something we were about to do here in the next couple months, we've just been waiting on some money to come through), and we were anticipating her being relatively easy about it since she's been playing nice lately, but of course this could blow all that out of the water if it comes up. Anyone have any advice or suggestions on how to handle this?