I found it helpful when I had my pre-school DGD all day to have lots of activities planned. It didn't matter if we didn't do all of them, but it meant that I wasn't searching for things to keep her occupied.
I always included going out - for a walk or to the shops - as getting ready adds to the time that the whole thing takes. Certainly getting out somewhere they can use up some of their energy might help. A new comic or crayons was useful to provide interest on return. We also used to take a picnic lunch into the garden when the weather permitted.
Some cooking or some arty crafty activity was useful for me, too.
Do you have any friends or relatives who could cope with a short visit which might also help to break up the time?
You will obviously know the things that the children like to do much better than me, but my initial comment about planning stands - have stuff ready to use and break up the day with different activities. Try, too, to get them to have a quiet time if you can!
If you're anything like me, it'll seem interminable, but it'll cement your relationship with them.
