I know exactly what you mean! Our family is exactly the same and DS is 27kg and was 5 in October.

We've been overseas and has never been checked as far as BMI but I know that it would class him as overweight.

I'm a relatively small person but weigh more than I look so I know he took after my side of the family. My dad is a big man though so I'm very aware of keeping DS healthy and active. Much easier now that we are back in oz.

It a hard one because you just don't want to cause body image issues either.

They are all so different. DS and DD are polar opposite. She will be 3 in May and hasn't even cracked 12kg yet, which DS had done by 12 months. They eat the same things too.... So I would hate DS to feel bad about himself because its in his genes.