Drawers filled with child-safe items
When my kids are home on a rainy day or I just want to entertain them in some way, I let them pick a cabinet or drawer in the kitchen and we empty the whole thing. The kitchen utensils drawer or one filled with tupperware storage containers or plastic cups are their favorites. They sit around the 'approved mess' and go through each item one by one. Piling them, grouping them, counting them. They ask what the things are used for and build towers. It's a great way for them to explore every day items. They also feel like they are doing something they are not usually allowed to do, so they are thrilled by that.