My son weighed 3660 g born and gained weight very steadily. At 7 months he was 10 kg! Then at 8 months he started crawling and at 10 months walked - these events seemed to signal a slide backwards in the weight stakes. Losing 1.5 kg over his 2 months of increased activity, he has only just returned to the weight he was 10 months ago.
I have had lots of explanation as to why this happened - but I continue to worry about it. He now falls under the 50 %ile in growth (down from the 90 %ile in the pre-walking days).
He is very active...but I can't help but to wonder if there is something else going on?

Hi Lousie,
My 2 yr old weighed 3.88Kg at birth and stayed consistently the same height above the graph until she started to crawl at 9 mths. It took another 9 mths after that before she actually hit the graph and now she remains constantly on the 97% mark. I'm not too worried as she's very active and is above the 90% now in height. For the first 12 mths I was told that she was being overfed (although she was on formula and we only gave her what was prescribed on the package) but the nurses were happy with the amount of solids she was consuming.
She ate poorly from 18-24 mths which seemed to be while she was getting most of her teeth. It has only been recently that she has stopped eating like a sparrow although she still has days where we struggle to get her to eat.
All I can suggest is that you take him to the GP and ask for some tests or a referral to a paediatrician to find out why your son isn't "thriving".