I made a lot of these on ebay for boys and girls. Very cute, but it got to be a pain trying to find overalls in the right sizes and the thick denim and pockets were very hard on my machine. Then I moved on to the birthday dress (more on that later). Then I made this for a friend and I thought it was such a cute design for a first birthday that maybe didn't have much of a theme or a sweet little family party.
My inspiration came first from a shirt I saw that was a birthday monkey that was just a monkey face with a party hat. Then I had an extra pair of bear slippers from Christmas (weird, I know) and so I thought that idea could be easily changed to the birthday bear. I got the bear face design from http://www.pegasus-embroidery.com and then I just used some simple shapes I already had (I believe from embroidery mall) to create the party hat. I left the onesie un-birthdayed so it could be worn after the party as a shirt.