I suspect that there’s a weird trend in superhero comics where whenever a superhero gets a biological younger relative at all it seems writers don’t know what to do with them. It’s like by the time they show up, they often almost always end up being raised by somebody else. Supergirl is Superman’s younger cousin but she got raised by the Danvers at least in the older stories and eventually Lana Lang.
Cable may be biologically to both Magdalyne Pryor and Jean Grey and was raised by those two and his sister Rachel but also ended up with the Askani or something. Rachel herself got raised by Ahab (in his own twisted way) and Cable’s doppelganger X-Man got raised by Mister Sinister and then spent time on his own.
(Somewhere online, I read there that Jean Grey’s an objectively bad mother.) Bart Allen is Barry’s grandson and whilst mentored by Wally West, he eventually hung out with the more distantly related Max Mercury. At other times whenever superheroes do get biological younger relatives, often their own children they’re eventually never to be seen again.
Stephanie Brown had a child but they got adopted and practically written off as to never be seen again. Same with Tigra and Rahne Sinclair’s children. (I actually think we could’ve gotten stories where Tigra takes her son on hunting and fishing trips.) This may not always be the case for some characters as there are others who do bother looking after them.
Most notably Mrs Incredible and Invisible Woman. Probably one of the Ant-Men and Wally West too. Another trend’s to render a biological younger relative nearly unrecognisable. This has happened to Supergirl in the 1990s and it’s only now they reverted her to being Superman’s biological relative again. Cable went from being an innocent child to a cyborg old man.
Rachel Summers has been made into an old lady (though that didn’t last long). Illyana Rasputin has gone demonic. Not to mention ageing them up real fast, this has happened to Cable, Rachel and Illyana and possibly Supergirl to a lesser extent. (In that she aged more gradually than they did but still seemingly faster if because Superman never seemed to age at all.) Superman also has a son and he also got aged up.
Bart Allen’s also stated to age fast. That still proves my point that superhero writers seem to have difficulty writing superheroes as having families, let alone get them to actually be involved in their younger relatives’ lives more often (or at least substantially so). Admittedly Disney and JJBA aren’t always any better but at least they actually do bother looking after them even if they sometimes screw up.
Though that would be that superhero writers do tend to prefer unrelated youngsters to biological relatives as the former are easier to self-insert as whilst with biological relatives there’s often the dilemma of trying to deal with them at all.