Go ahead the bulkhead can comfortably fit 2 persons for dining so long as your kid has a ticketed buisness class ticket for himself. One on the chair and one on the ottoman.
both dining in the same seat is also fine as the seat is Super Wide
always done that with my +1 in On the 77w and a350 J... just have to be careful of your movements as all the plates are squeezed together on the table 😂
just take note of the seatbelt sign if its on then everyone has to go back to their own seats.
ps: the crew might ask your kid to be on the seat and you on the ottoman though as some of them have said there are no seatbelts in the ottoman and kids might not be able to balance themselves properly sitting half angled on it 😄