I find the best lessons Havvie and I do are the ones we stumble upon accidentally. This happened to us yesterday when Havvie was playing with some fridge magnets on the kitchen counter and one of them stuck to one of the spoons that was next to it.
This was a great opportunity to introduce the concept of magnetism in a very basic form. We proceeded to take out a bunch of cooking utensils from our kitchen drawer and see which ones were magnetic and which ones were non-magnetic.
It was short, sweet and lots of fun. Even I learned something as I found out stainless steel can be magnetic based on the way that it is formed, which is why some of the spoons were magnetic while others were not. This simple 10 minutes of experimentation added some new vocabulary, classification and provided a foundation for science that we could do later on.