My little guy (20 months) is very small as well, he is in the 4th percentile. The doctor expressed concern early, but since at all of his checkups he has remained in the 4th percentile, they are not worried at all. He will just be a small guy, 5'6" ish is what they see him being at full grown. That is fine with me because my husband and my whole family are all very small people. He did go through a spout where he was throwing up a lot and not keeping anything down, and he had diarrhea and no one seemed to care to help me figure out what the problem was. So we saw a Pediatric Gastroenterologist and he was concerned that he had actually lost weight and gone below the 4th percentile on the growth chart. I was very worried, but his tests turned out normal and he has since gained the weight back. The way I look at it is, if YOU think that something is wrong and the doctors show no concern and they are not worried.......but you, in your Mommy gut, really feel like tests need to be done, then you should insist on seeing a specialists or INSIST that tests be done. Even if there is nothing wrong, which there probably isn't, at least you now have the peace of mind that all of the possible things that could be causing his slow growth are all testing negative. That's what doctor's are for, in my opinion. If you are concerned and the doctor's aren't, you can either trust them or go with your instinct and get another opinion or insist on testing. Ends up costing money, but, for me, I wanted the peace of mind. On the other hand, remember that ALL children are different and they will all grow and develop at their own rate. And there is nothing wrong with being small. My Dad used to tell me when I was little and I got picked on for being the smallest kid in school that "Good things come in small packages."