I also got the idea for this caterpillar cake by browsing this site, so thank you, coolest-birthday-cakes.com!
My twins were turning 3, and I wanted a cake that would work for both a boy and a girl, and since they love the Baby Einstein caterpillar, I got inspired to do this, even though it was my first elaborate cake. I was intimidate at first, but it turned out easier than I thought.
I used 3 cake box mixes, vanilla and chocolate, baked all six domes (Wilton ball pan) ahead of time -2 weeks before - and froze them til 2 days before the party. (Use the "press and seal" plastic wrap, with a paper plate under the cake, cut out just to the size of the dome.) One of the domes I used as my practice cake, a week before, to boost my confidence, which was a great idea. It gave me an idea of how much time I was going to spend and what I wanted to do with the icing, the head and etc.
I used store bought vanilla icing (5 containers) and colored them with Wilton's icing gels. My kids loved to "help" me with this part. I was going to pipe the domes with the star tip, but it was going to take way too long, so I just frosted them smooth, then using the flat part of a spatula, just tapped the icing, to form "spikes", so perfection was not an issue, thank God! I used the left over icing to make dots on each dome, with ziplock bags, cut at one of the corners a tiny slit. The eyes are brown M & Ms, the mouth is a cake decorating gel (Betty Crocker - from the grocery store), the feet are small chocolate truffles, and the antennas are cherry lollipops, which I colored the stick with a red marker to match.
The "Happy Birthday" candles I found at Target, then used scrapbooking paper letters to make their names, sticking them with tape to tooth picks.
I frosted them the night before, which took almost 2 hours, and assembly took less than 5 minutes, an hour before the guests arrived. Everybody loved it, above all, my kids couldn't believe their eyes. Their expression made all the effort so worth it. I'm already looking what I'm making for their 4th birthday!