You can use a silicone round baking pan for your ice cream. Just grease it really good then put the ice cream in it and freeze (or line it with wax paper, that way you can lift it out). It'll turn out the shape of the cake and will come out easy.
I used this for my son's 3rd birthday party. It was very easy, I also did not cut the layers just - cake - ice cream - cake. I used the whipped cream frosting Whipped Cream Frosting. I used a vanilla cake mix with chocolate ice cream and chocolate frosting. I crushed oreo cookies and made a construction scene on top. It was a hit!! However, I have to say that the cake was more popular with the adults because it wasn't that sweet. Next time if using this for a kids party I will use some type of kids ice cream.
Cutting the cakes in half didn't make sense to me. I left them intact and put the layer of ice cream between them and frosted the top only.