She does the whole cute manipulative baby voice And says daaaaddddddeeeeeeeee because its how she can stick her hands out for money after the rare occasions she visits her dad

Record her saying it to show her when shes a teen lol. 

Also, I feel your pain. My SD finally graduated to saying dad instead of daddy. It started being dad and mom instead of daddy and mommy on school papers, so I'm guessing she got made fun of. Unfortunately she still uses the fakey "I'm so cute" voice all the time. 

There was a girl on my daughter's softball team that was calling her dad (the other assistant coach) Dada. I deadpanned looked at her and asked "Did you just call your father Dada?" she smugly said yes. I told her "Knock that crap off. You are not 3 years old. I don't want to hear that on this field again. You are embarrassing him, me and the rest of your team. Grow up!" She pouted and walked off but she didn't call him "dada" around me any more.

Feel free to substitute field for house and team for family!

but I'm the bad guy if I tell her she sounds stupid 

This is how kids speak to each other; not adults. I wouldn't be okay with someone telling my skid he/she sounds stupid. There are more tactful ways to say things.

Does "Dada" have a problem with it and has he said anything to her about callilng him "Daddy" or "Dad"? Maybe he likes being called "Dada" because doesn't want his wittle pwincess to grow up....

Did you seriously call an 8 year old stupid for saying "dada?"

I would have a big problem with anyone speaking to my child like that.

Skid, who’s 13-years-old, still calls DH “daddy.” It’s cringeworthy, if I happen to be subjected to hearing it. 

Just last year he stopped responding to her “daddy” with a “yes, baby.”

Deep breaths..

Dada... mama... bonus mom.. erp.. think I just went blind from my eyes rolling back into my head...lol.

Seriously though.. I know it grates on you and sounds immature.  But.. honestly, the girl is 8.. .it's not like she is 25 and still carrying on like that.  Junior High is likely to take care of THAT.. haha.  I mean.. yeah.. I konw some people still revert back to 6 years old when talking to daddeee and mommeee but most people grow out of that stuff eventually.

Yes.. you would be the bad person for calling an 8 yo stupid... she may be an immature 8 yo.. but you are an adult and "should know better".. I know you are just venting here.. but you do realize that it's not just "sucking up".. but as adults we should be holding ourselves to a higher standard than an 8 yo.. haha.

wow isn't this a hot button subject!  i can understand OP's irritation - it irritates me to no end the way yss drags out NNNNGGGGDDDDDADDY.  but all the kids have always called him 'daddy' and they always will.  hell, my 79 year old grandmother still refers to her mother as 'mommy'.  to each his own.  for me personally, it's not the word, it's how it's said.  the baby voice would drive me APE-SCHITT CRAZY.

with a side of cutesy.   Only works if the BIOparents ENCOURAGE it!!

When she has JUST come back from her mothers 5 day visitation. It takes a day to detox, er, decompress. I notice when she speaks to me, she changes, and speaks correctly because thats what I do, and sometimes correct bad diction. Its just ingrained in me, I dont correct to be downgrading someone - more for being "helpful".

But SD13 doesnt call her father daddy - its dad.

The older one would use the "dadeeee" when she wanted something and had her hand out. Drove me nutzo.

Nah I get it, it's annoying. DH used to call Spawn pumpkin, and then he started calling me pumpkin. I asked him to stop, I didn't want to be referred to as a term of endearment he had for his child, that felt gross.

I am still waiting for my OSD13 to stop with both Daddy and Mommy and graduate to Dad and Mom. It's totally weird to me. I can't quite explain it, but it feels like she is playing to their egos in a way. Even though she doesn't use the baby-talk voice (99% of the time) it feels mildly manipulative... or perhaps just a strange coping mechanism to create connectedness between her and them? Something about her voice changes when she says it and it just rubs me the wrong way sometimes. YSD8 uses Daddy and Mommy but it sounds completely normal and in no way affected when she says it.

Anyway, my skids aren't even that bad and I still get annoyed, so I get your frustration.

I would find "Dada" annoying too, if it's part of a general "baby talk" thing that she does.  Daddy would still be fine at 8, for me, but Dada would be annoying AF. Not much you can do if DH is okay with it though.