my firstborn was like this. She was always either at 0-5% or below on weight and height. She ate like a horse and hit all her developmental milestones just fine. She resembles her paternal great-grandmother more than anyone in the family - very tiny and petite. The thing is I'm 5'10" and no one would confuse me with a petite person :tongue_smilie: So the doctor would look at me, then look at her chart, then look at me, and wonder if there was a problem.
I hope that all it is for you too.