My 8 year old is not putting on weight

I am concerned about my son not putting on weight.  He is average heighth among the kids in his class, but very thin.  I try to push him to eat more and at the same time I think I'm making food too big of an issue.  I don't want to give him a complex about his size.  My wife and I are both above average sized people.  It worries me that I am not doing enough.  He has been at the same weight for a year now.  Any help would be greatly appreciated.

[Renee Radenberg]

His weight is below the 5th percentile and his height is just below the 50th percentile for his age. Engage him with preparation of food. Have him help you set the table or do something for the meal. Children love to be a part of making food. Hopefully it will increase his interest in food. Suggest giving him milkshakes (ice cream, fresh fruit or frozen fruit, milk) or yogurt smoothies (yogurt, fresh fruit, and frozen fruit) and for additional calories, protein, and vitamins and minerals a few times a day. He can help make them, too. The most important thing is to RELAX. Let him eat what he wants. Slowly introduce new foods, and if he does not want it, do not make a fuss over it. Let it go and enjoy your meal. Try again in a few weeks. Hoped this helped you.