booksmook!!! On paper thats how things should go but in the real world it isn't. When I Shanna was born me and my brother we worried because at 6 mnths she was in the bottom 17pertentile..but the pediatrition wasn't worried. She was just small. Now she's 3 and a half and has almost caught up with the rest of her age group. if the doc doesn't see anything wrong then you shoudlnt worry about it