Depends entirely on the anime.
Lots of action, etc.: dub
Lots of dialog: sub
Discussion
Sounding kinda sus right now explain yourself
Lots of action means I can't focus on reading so I need the dub. Anything with plenty of dialog lends itself more to sub. Truthfully, if I could get a combo I'd be thrilled. Also, sometimes the kid watches and he's only 8 so the dub helps there too. But when he gets older, he's rewatching the classics with subtitles.
Watching dub anime with your kid is valid 