Both my kids were skinny for their height. If you saw my 6yo you'd understand.
My 3yo was on the 5th centile for a loooong time. There was a thread on this a while ago, and many of the mums had been referred to paeds/dieticians etc about their children's weight. I never was. Don't know if it's my 'don't mess with me' attitude or not
My little guy hardly ate too. But, from previous experience I knew he would when he was ready. He was also still BF and was weeing/pooing and meeting all his milestones.
Mummy intuition will tell you if you need to do extra or not.Is he eating high cal foods? That's probably my only suggestion.