For the morning they will more or less follow along with everything else you are doing but make use of them as helpers so they don't feel like they are a student but instead a teacher's aid even though what is really happening is everyone is sitting in a circle singing nursery rhymes - but they are holding the props or moving the feltboard pieces for you. Let the older one read to the little ones.

For the afternoon when it is naptime it is ok to tell them that they have to spend the fist hour doing something alone quietly.

You can also make use of them to create learning resources for later such as having them construct a spaceship out of boxes and spend all afternoon decorating it and then everyone gets to play in it when the little ones get up.