enjoyable and mentally stimulating activities for toddlers

I am a part-time teacher of toddlers and pre-schoolers and I can tell you that from their perspective, doing things reptitively is a good way for them to learn. If you see them being occupied by an activity in which they are able to focus and holds their attention for any span of time, then there's no need to introduce any new activities until you see them becoming bored. My children often got bored with their toys so I would rotate them by putting away a few in a closet for a few weeks and just let them play with a few interactive toys. Then I would take those away and take out the other toys. To them, it was like getting a new toy every few weeks. They often ejoyed taking out pots and pans and that would be a good source of entertainment for them, especially at bath time. In the summer I would put the pots and pans out on the deck with a bowl of ice cubes and they would be busy taking the cubes in and out until melted (good pre-math and science activity).