Don't change a thing....sounds like it's all going PERFECT
DS was a healthy chubby(ish) little bubba, then once he started walking he slimmed down a bit and now he's perfectly healthy with just the right amount of weight on him.
I think it's good if they're a bit on the chubby side so that if they get sick they have fat reserves to help get them through the illness. Once they get more mobile they slim down a bit.
Keep up the great work