Take a baby yogurt cup and stick a Popsicle stick (or plastic spoon handle) through the top. Place in freezer overnight and you've got yogurt on a stick. Just run it under hot water for a few seconds to separate the Popsicle from the cup.
If you're looking for a simple activity, just hand the goodies over to your preschooler and let them compile their own pops. Nothing is more delilicious than things tykes make themselves.