toddler make choices about the little knickknacks that you need to decorate the nursery.
if you feel he cannot make the right choices, you can always boil down the number of choices to two or three and then let him make the final decision.
the idea is to keep your toddler involved in almost all arrangements to be done for the arrival of the new baby, and let your toddler remain involved even after the new baby has arrived. 