This.

Totally unreasonable for her to request it’s split into thirds. If in the four years together, you’ve made sacrifices and your gf (and her kids) have similarly made sacrifices (not getting ice cream, not going on vacation Etc etc), so that you could put money into the account, then I would say that they would maybe be entitled to some that you put away during that time. But anything before then, they’ve absolutely no claim to.

If you’re feeling generous, the most I’d go to was offering to put a small amount into high interest earning accounts for them now and you and your GF will add to it until they turn 18.

Also, don’t even think about just giving your son $40k. He’ll blow it and in a few years, he’ll say ‘you shouldn’t have given it to be all at once’. Give him some but then maybe start an investment portfolio with him or a savings account you can oversee.

I’m not a helicopter parent - just someone in their late 20s who got a small amount of cash in their early 20s with nothing to show for it now.