You could ask the parents what sorts of things they like to do. Is it at a house with a yard, where you can let them run around, or toss a ball around? Do they have toys or games?
You can also have them help you prepare lunch -- sandwiches, fruit salad or green salad. Make rice krispy treats (which is SUPER easy -- melt butter, then small marshmellows over low heat. Then mix in the crispies.) At those ages, especially the girl, they can probably mostly entertain themselves.
Maybe bring a movie that kids like, if you have any.
They will most likely find things to do. You are just the monitor.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.