How do you keep cool in the heat when you are indoors?

I have myself and a one year old and a four month old and its 31 degrees out right now(canadian not sure what that makes it in the other type of degree)

I have all the windows open and the fan going but its still majorly warm.

Im concerned about the baby mostly, since overheating can be very bad. I can put Mya(the one year old) in the tub from time to time but I can't do them all at once and certainly I wouldnt FIT in the tub with both of them( I barely fit myself, haha)

So what else can I do to keep cool?