If he's healthy and active I'd say he is having enough. My two are like others have said, some days they eat a lot, some days next to nothing. They are both growing taller and gaining some weight, they are active and sleep well so I guess they get enough! I agree that they are good at self regulating (a skill I lost along the way somewhere
) and do seem to know what they need.
DD has really slowed her weight gain down in recent months but she is still on her centile, or close to so it seems to be what she is "supposed" to do now. I keep an eye on the kids weight at home, DD has lost a couple of lbs but she has had a chest infection so literally ate nothing for the best part of a week so that's not too surprising.
Laura