My 13 month old DS has diastasis recti, separation of the abdominal muscles. I know he has it because I have it myself (alas!) and therefore I know how to spot it - telltale ridge down the centre of the stomach when leaning back etc.
He isn't overweight at all (he's about average height and weight) but his stomach sticks out a lot. Some trousers are really tight on him. It's much more noticeable in the evening and after he's eaten, much like mine.
I read that most infant diastasis resolves by itself by about 9 months, and most of the remaining cases have resolved by 3 years old.
Does anybody else have experience of infant diastasis recti?