Physical milestones typically refer to your child's weight and height. For boys the average weight for a two year old would be anywhere from 24-29 pounds and 33-36 inches.
The average weight for girls at the age of two would be 23-28 pounds and 33-35 inches tall. If your child falls under or over these ranges it may not necessarily be a bad thing. However, you might want to discuss that with your child's pediatrician and let them know to make sure that your child is developing on track. While you may notice that in the playgrounds or at school your child may be shorter or taller than others and you may be concerned as to why that is and you may think to yourself, "Well I don't recall being taller or shorter than anybody else. I feel that I was average. I don't know why my child is." It's okay.
Kids develop at a different rate and sometimes girls even develop faster than boys typically and they might even catch up to boys.
So what's really important is that you're monitoring how your child is growing in terms of weight and height and that means that speak with your pediatrician and make sure that you have a copy of their growth chart so that you too can continue to monitor your child's growth and height.