Nope I wouldn't worry. Some bubs just don't put on weight like others. That whole percentile thing is just mean to us mums! Gemma was always in the lower end and at 12 months I was told if she didn't put on more weight she'll be underweight. Well poo to them cause Gem is a happy, healthy smart toddler that just is very slight for her age, always has been. As long as shes putting on weight each week then I don't see a problem. And you said she can do alot so I wouldn't worry. Babies progress at their own rate hun. Your doing a fab job!!