I asked my daughter, age 8, what was her favorite part of Geocaching. Her reply was "finding the cache". I asked her if finding a toy in the cache was her favorite part, she said finding something in the cache made it a little bit more fun but she also likes finding micro caches. We always let her decide what to take and what to leave. There seems to be no pattern to her selections.
I know some people are very opinionated about what should be left in a cache and my opinion is that as long as it's not trash and it's family friendly I'm happy and so is my daughter.