Netix - my DS turned 4.5 today, he is 15kg and 97cm tall. He is in the 5th percentile for weight and 3rd percentile for height. He's a runt. However he is growing at a steady rate, has plenty of energy and is healthy and fine. We had a paed checkup (not due to weight or height) a week ago and the paed was very happy with his development / growth etc. Some kids are at the bottom end of these 'average' sizes, maybe its just our kids

Unless he is dropping into lower percentiles and he really isn't eating properly, I wouldn't worry to be honest, sounds like he is just a slight fellow. 4yo are particularly fussy with food too! I was a skinny kid too, I think he gets it from me, once I hit my teens though - Pffft! My DD is catching him fast, she is 15 months and probably about 11 kg, she'll match his 15kg soon enough!!