This is  more common than you think.  My daughter is at the 5th percentile & has always been small. I have posted in the past asking other parents info re weight, height & type of meds trying to see if anything is in common....I had several responses & found out that my daughter is not the only tiny one.  Her birth parents were average height, (we adopted) so genetically she could be a lot taller. An Endo we saw suggested we may use growth hormones once she is 4yrs old if she is still small. She will soon be 4 so that may be an option. Not sure what we will do. She is healthy, active & doing everything on par with others her age but only 28 lbs and 33 inches tall. We get a lot of mileage out of her clothes & shoes!!! I too would like to find out more about this. Thanks for posting.