When the little ones aren't interested in what you've planned?
Sometimes this happens with my DS5 and DD3. They just want to play the great game they have just made up rather than sitting down to read like you have planned. At this age I allow them to continue their play asking questions about what they are doing which may lead to discussions on certain topics.
For the past few days DS5 has been playing with his dinosaurs and his dinosaur activity book. So we are using them within his subjects.
In Science we froze the dinosaurs which gave him an understanding of solids & liquids, reversible/irreversible changes and then excavated them, in Literacy he used them to 'stomp' on the words as I call them out, which led to making a simple dinosaur storyboard, in Art we used them to make tracks whilst mixing up the primary colours.
So don't worry if they just want to do their own thing they are still learning new things all the time and you can adapt your plans easily to their interests, which is one of the many reasons I don't plan too much in advance and one of the many great advantages of Home Ed ;)