Get my son to gain 10 lbs.?

is there a supplement that will fatten up my 2year old son?I want him to gain about 10 pounds and I will stop worrying so much.Is there a formula for toddlers?He doesnt eat very much, I hide baby veggies in his mac n cheese because thats all he ever wants to eat, but he is only in the 25%th percentile for weight and the 75th percentile for height, which I am not concerned about his height be cause i am very short(only 5ft. and 28 yrs. old lol) but I am concerned about the weight because when he was born he was at the 50th and now he is at the 25th percentile.Does anyone think this is ok or should i be concerned.I just moved to AZ so his dr. is not familiar with him and only saw him once and didnt act concerned, but shouldnt he at least ahve recommended a nutritious supplement?I know this is more than one question and all feedback is appreciated unless it's mean.