My cat ended up pregnant after escaping and had 3 very healthy kittens, they were all weaned and litter trained by 7 weeks old so 2 of the kittens went to their new homes with people I new and trusted & I kept the other one.
Kitten came back to me yesterday as the other person cats didn't get along with him so I agreed to him coming back rather than him going to a stranger, so now I have 3 cats and two kittens 
The thing is he is half the size of his brother as he looks more 8 weeks old rather than 12 weeks and 3 days, he is eating and drinking and using the litter tray, he is very clingy and all he seems to be doing is sleeping with the odd 5 minute fight with his brother - none of them recognise each other & the mum is very wary about him.
I'm not use to a clingy cat as mine all like to do their own thing & him being half the size of his brother I'm not sure what to do.
Will my female cat (his mum) get used to him as I really don't want to have to find another home for the poor little thing.
Also what's the best food to help him gain some weight as he is a skinny little thing
He is a maine coon cross if that's any help and he is the only one out of the litter with all the maine coon traits, very vocal etc