DD3 is starting to pick up some simple arithmetic (maybe from watching PBS kids and listening to bigger siblings). Our conversation:

DD3: What's 2+3?
Me: What do you think 2+3 is? [A week or two ago I would just answer the question. Now I'm checking she really knows.]
DD3: Five! Look! Five fingers! [Holding up one hand with 5 fingers.]
DD3: What's 5+5?
Me: What do you think 5+5 is?
DD3: Ten! Look! Ten fingers! [Holding up two hands with 10 fingers.]
[Then DD3 starts sucking her thumb.]
DD3: Wopf fibe pwuf four?