I think
@John Andrews Stan and I both come from a culture with a lot of big middle- and upper-middle-class families. So maybe he/she can confirm or tell me I'm off base here.
It has stuck out to me for a long time that Nick says all of his kids are 100% healthy and fine.
Frankly, that really doesn't happen very often. If you have five kids, you're probably going to have some issues. If you're lucky, maybe one or two with dyslexia, a stutter, side-swiped by the Aspergers. If you're less lucky, you have a kid with serious health issues or major behaviours.
Nick lists every activity they do so he's not worried about their privacy. But not one kid needs a tutor? No specialist appointments? No OT/PT/SLP? Nothing? For FIVE? This would be a lucky streak for two typical parents who do everything right. For someone raising their kids in chaos, it's unheard of.
It's significantly more likely that the kids are straight-up neglected. They have very serious needs, they're not okay, and they're not getting any help for it because he's neglecting them in favour of coke. So basic stuff that typical parents would have investigated (like why they're so very short) just gets ignored and he tells everyone how FINE they are.
Also pretty sure what Aaron was hinting about is that the child has extreme behaviours and when he heard about the cocaine, that made sense to him. He means that Nick's favoured daughter is completely out of control.