ArithmeticWrite your own
Invent a question that fits, then answer it yourself.
“A shop's coins are 1c, 4c and 6c. Write a question of your own whose answer is exactly three coins.” Every other sheet asks a child to answer. This one asks them to ask.

The answer key prints on a separate page.
NAGC, NCSM and NCTM propose a ninth practice beyond the usual eight: solve problems in novel ways, and pose new mathematical questions worth investigating. Nothing else on this site does the second half, and paper turns out to be unusually good at it — inventing a question needs no marking software, only a way of telling whether the invention works.
That is the part an exhaustive engine can supply. The key does not print one answer; it prints the whole space. With 1c, 4c and 6c the amounts needing exactly three coins are 3, 9, 11, 13, 14, 16 and 18, so a child who wrote “how few coins make 14c?” and a child who wrote “how few make 9c?” have both done it right, and a parent can see that at a glance without having had either idea.