The birthday theme was "The Wheels on the Bus" for my one-year-old twin grandchildren who love the song. I made a school bus cake out of a pound cake type cake and baked it in a double loaf pan I had bought years ago (it could be done with 2 loaves). I cut off about 1/3 of it, so it would look more childlike, then I sliced off the domed top part of the cake to use on the roof and the hood (you could just leave the hood part on when you slice if you have measured how much to leave.
Make a wooden base which has wooden half wheels and make it wide enough for the cake plus icing. I iced the bottom of the cake (plus the domed part of the hood) with buttercream decorator icing before I placed any of the plastic cab and passengers on the cake.
The plastic cab window section of the bus is the molded plastic part of the container for Q-tips. The riders are Little People by Fisher Price. The Little People are sitting in a wooden base that has been drilled with holes for them to sit in. This base has been cut to fit inside the molded plastic and set on top of the iced bottom part of the cake. I had to use dowels for support, but it was because I had to travel with the cake
I iced the domed top part of the cake before I placed it on the plastic cab window section, because I was afraid I would mess up the windows. I used 2 large spatulas to slip it on top of the plastic cab section. I then used my decorator bags and tips to make straight edges everywhere, and to add the window dividers and bumpers.
The wheels were Oreo cookies with silver paper circles for hubcaps (use icing if you are concerned a child might eat this). I also used clear acrylic beads for headlights and red acrylic beads for taillights, but these could be made from icing or candy circles.