I like the brown. Remember that a child cannot identify colors until taught. If you have ever given a child a box of crayons before they learn colors, they invariably will pick out the darker colors.
My vote is for the orange, makes the blocks look like they are floating. And bright is just right. Then bind it in brown or blue. Fun and great pattern for the new little one.
I think you need the blue border (to really make it pop)first, then the orange and I would have brown on the outside because that is where it will be handled the most and the brown will not show dirt etc.
