Low weight percentile but incredible milestones...?

One of my daughters didn't feed much either. She was 3.5 kg at birth and only weighed 8 kg at 18 months old. My other one put on half a kilo a week and weighed 7kilos at 12 weeks. Both are totally normal - they're 18 and 20 now. Oh, and the second was sat in my lap holding my hands when, at 12 weeks old, she suddenly stood up. From that point the only game she wanted to play was bouncing up and down on her legs or trying to walk whilst being held by the hands. There is a huge variation in what is normal for babies; as long as they are healthy and happy, making progress and gaining weight there isn't much to worry about (doesn't stop us Mums tho)