T.G.
Hi K.,
The $1 store, 99 cent store, or big lots often has plastic characters that you can put on cakes to spruce them up. That way if you are not a cake decorator you can still have a cute cake just by smearing some icing on it and placing some figurines. Michaels and Hobby Lobby have character cake pans if you choose to go that route and all you need to decorate those is usually a star decorating tip, one pastry bag, icing and some patience. I decorate cakes and if you need an icing recipe feel free to email me and I can pass a simple one along.
You can also get your party favors, plates, cups...you name it.. from any one of those discount stores for very inexpensive. Until they are about 7 years old, it seems to be quantity over quality. Give my 2 year old a box to play with and she is a happy camper.
We went to a party recently for kids 5 and under. My friend had asked to borrow a number of baby pools. She had about 7 pools set up all over her yard and all the kids had a great time running crazy in the yard and in and out of all the pools. They served cold-cut sandwiches on rolls, chips and cake. Her theme was Nemo. The kids hit a pinata filled with candy. It was simple and fun. The adults had a great time mingling and watching the kids.
At your sons age it doesn't need to be complicated. Keep it simple so you can enjoy the party too. Good luck.