I think a member here has had the same case, Joe. I just forgot his name. Well, that was when it was still the old rule, but his stepchild was about 18 (or older, I really can't remember exactly) and still dependent on them.
that could have been me , but that was yrs ago, my stepson turned 18yr before his mom could apply for ILR, so i made sure he was still dependent on us when he and his mom applied for ILR