Math is Hard
I thought I knew arithmetic until I found the Disney Magic Math Machine, a book of illustrated addition and subtraction problems with a handy cardboard mechanism for looking up the answers in a table. It starts out innocently enough on the front cover:

2 cherries plus 6 cherries is 8 cherries. I get it.
But then, inside:

2 peaches plus 3 pineapples is... uh... two peaches and three pineapples? Five fruits?

7 beach balls minus 5 roller skates. I have no idea.
At least the back cover brings the difficulty back down a bit:

8 soccer balls minus 6 soccer balls. It's obvious from looking at it: The answer is 14 soccer balls.
Picking on the Machine is fun and easy, and I should probably leave it at that. But I can't resist the opportunity to mention a few of my favorite books on numbers for small children, because they nail the difficult task of visualizing these concepts:
- The Usborne First Book of Numbers, by Angela Wilkes and Claudia Zeff, illustrated by Stephen Cartwright. (Out of print.)
- Anno's Math Games by Mitsumasa Anno. 2, 3.
- Domino Addition by Lynette Long