This is Shaggy and Velma from Scooby Doo (my children, ages 4 and 2). My son is obsessed with Scooby Doo and said he wanted to be Shaggy and my daughter wanted to be Velma.
So I started looking for costumes, they don’t make them that small so I had to make them myself. Then I thought that I would also make the Mystery Machine so everyone would know who they were. I just used a shopping cart and drew on poster board, then painted it and glued it onto the cart.
I ended up putting Scooby Doo on the front and then cutting a hole in the top so they could put their candy while trick or treating.