Here's a quick list to help you get started with sculpture, no matter what age you're working with.
Materials to Sculpt and/or Carve
Bread & glue clay
Wax (cheap candles)
Potatoes, turnips (root vegetables)
Plaster (dried, to carve)
Butter knives, forks, spoons (use metal and heat in warm water for wax and soap carving)
Add in: sand, glitter, buttons, small plastic toys, etc.
Connect parts of sculptures with toothpicks or straws.