One Red Personalized Onesie. Choose from 6, 12, 18, or 24 month sizes. Celebrate your little one with our adorable Red Personalized Onesie! Simply enter your child's name in the 1st Line of the Product Options to the right, and we'll print it on the onesie in white lettering. Browse our fantastic selection of 1st Birthday and Kids Party Supplies, from tableware to decorations, and make your child's birthday extra special.