how can i make my child gain some weight

Hi, I have a 6 years old son and he looks very thin. All our friends keep telling us that he looks too lean for his age.
The problem is, that he doesn't like to eat a lot of carbs and he is very active (does lots of sports).
He also likes eating several small meals a day (6-7) instead of 3 main meals.
What foods can i give him to help him gain some weight?

[Renee Radenberg]

His weight is just below the 50th percentile and his height is on the 90th percentile for his age which indicates he is normal. He has a taller stature for his weight which makes him appear thinner. He is not underweight and eating 6 meals a day is fine. If you are very concerned, then suggest giving him milkshakes (milk, ice cream, and fruit blended) for additional calories and protein for weight gain.