Is it normal for little people to not gain weight when they start running round? I mean not gain weight AT ALL?? Below are his weights for the last year & I'm a little worried. He's gained only 1.5kg in an entire year, surely that can't be good? He has been walking from 11 months so for that entire time he's been a walker. Each time they were taken with a nappy only so it's not a clothing issue.

12 Months - 11kg
18 Months - 12.5kg
24 Months - 12.5kg

HELP!