I just learned a super cool calculator activity! Maybe you already know about this, but I was so excited to learn it! I am in the middle of reading Teaching Student Centered Mathematics by John Van de Walle. In one of his chapters he talked about turning the calculator into a fact practice machine.
Let's say you want your kids to practice their +5 facts. They should punch in +5= into the calculator. Then the child enters any number and says the sum of that number plus five before pressing = sign. They can try out other numbers and the +5 = DOES NOT need to be repeated. It will automatically add 5 to whichever number they push. Try it out. It is very cool. Subtraction also works with this nifty trick.