AI'm new to this site and I need help with choosing the right chocolate cake, filling for my son's third birthday!! Please send me your advice thank you!

I make standard buttercream  (1 c. butter, 1 c Crisco, 8 c. powdered sugar, 1T vanilla, 6-8 T. milk)  and add 4T of cocoa powder to it.  Everyone loves it and its very simple and shelf-stable.

So many options for filling depending on your taste:

Orange curd

strawberry

ganache

cannoli filling

dulce de leche

chocolate truffle

AThanks guys for all the help! Much appreciated!