I've got a little dynamo too, compact little thing. They're cute hey! He's almost 2 and still in 0's and some 1's.

I think just be positive about it, you might be re-educating people when you reassure them there's absolutely nothing to worry about. You could refer to petite adults like Kylie Minogue, Kate Moss or the Olsen Twins, last I heard people weren't complaining they were too small. Or if you were feeling a bit narky you could always ask something like 'do you think there's something wrong with her?' and hope they squirm. Thing is, being negative can make you feel negative and you don't want that.
If people won't leave you alone, you can always bring in the professional(s), like 'my doctor and MCHN say her size is just fine'. What are they going to say 'oh well your doctor's wrong?'