My DD1 was so tiny compared to DD2. They are fed the same way! DD1 was 2.9kg at birth, barely put on 80g a week and is still little... not that we have ever worried. DD2 was 3.8kg at birth, she was 5kg by 3 weeks! Part of it is genetics, I think as I'm small (165cm, 55kg before DD2s pregnancy) and DD1s Dad is a rake whereas DD2s Dad is not overweight but a more solid build, broad shoulders etc.

The main reason I think you can't overfeed them is because when I'm lazy and would rather DD2 just have a quiet feed for a bit or feed to sleep instead of rocking, she refuses. She only wants to feed when she wants to. Not sure how it would be different if they formula fed as I have no experience. How could you really restrict them anyway, it is pretty impossible so I just go with it and enjoy my chubby bubby!

DD2 already seems more active though! At 5w she is pushing up on her arms and legs with such strength, she basically came out holding up her head...5 chins and all hehe.