Costume looked cute on my 3 month old twin boys.  They seemed comfortable and I was able to have them wear a heavy sleeper underneath since it was very cold on Halloween this year(the costume fabric is very thin).  The only problem, one I didn't think of until it was time to put them in their stroller, is that there were no holes in the suit for seat restraints.  I ended up cutting a hole in them to make it work, but it is something to consider if you plan to wheel or take your kids in a car seat for trick or treating.