I think what was bugging me is the implied negative space between the left character's spine and the back of the couch.
There's also some inconsistencies with scale, I think. I think it's the main issue right now. Judging by your couch (usually 3' at the back), you've placed the "camera" at 4' off the ground. Doorknobs are also usually this height, but you've got one lower than that right next to the couch. The desk in the background is about 18" off the ground, half the height of most desks. I don't shop for furniture very often, so you'd have to tell me if coffee tables are usually 9" tall and 12" wide.
a, b, and c are head sizes, which seem to vary a lot. Kids of different ages make it hard to judge, though.
I think I misread the couch in your drawing; so ignore that draw-over. However, it seems super shallow to me.
Window panes should follow the perspective lines, too, and I'd expect a gap between the seat's edge and the shorts of the child sitting. Make sure the legs of the chair fit the perspective, too.
Observation: All the characters' heads are equally spaced.
I hope this wasn't too messy or confusing. Let me know if I can make anything more clear.