Which boy is which?

So who is who?

Liam was clearly bigger (Ben had sweatpants and a shirt under his outfit while Liam had nothing but a diaper) at this age, rounder, with chubbier cheeks, and Ben has more hair, but they are clearly brothers.

Then to show how much Ben has grown in the last year:

2010:

2011 (same costume on Liam but a different size....2T/3T last year and a 4T/5T this year):