Are they REALLY the same age?

Kaitlyn has a cousin, Brennan, who was born less than three weeks before she was. It was cute seeing the two of them playing together in Atlanta and interacting a little bit. They shared many things that week--toys, food, sippy cups, and even a stomach bug. However, one thing they've never shared is a similar plot on the growth curve! Brennan is trying his best to become the stature of a football player by early next year, while it appears Kaitlyn will be content to remain in her infant car seat until she graduates college.

My petite little girl only weighs 18.5 pounds (at 14 months). My goal is to fatten her up in the next month or two so that she can graduate to a forward-facing carseat in time for a big road trip we are taking in March. Any suggestions? I started the process by giving her her first chocolate marshmallow Santa. Despite the fact that she was desperate for a nap, she approved!