One Lion 1st Birthday Personalized Onesie. Choose from 6, 12, 18, or 24 month sizes. Celebrate a fun and furry first birthday with our adorable Lion 1st Birthday Personalized Onesie! This baby blue onesie features a friendly little lion design and sweet lettering that lets everyone know who is one year old. Browse our fantastic selection of 1st Birthday Zoo Party Supplies and animal themes, from tableware to decorations, and make your little one's birthday super special.