Superstition or Just Convenience

Was walking home from the bus-stop and I saw this little boy pulling on his grandpa's hands towards the playground. However, his mom and grandma were against the idea of him going to the playground whilst the grandpa was trying hard to persuade them to let the boy play a short while.

After awhile the mom sounded frustrated, and started telling the grandpa there are dirty things in the playground. When I heard that I wanted to laugh. Just exactly is the mom too superstitious or she is just using it as a convenient excuse to prevent the boy from going to the playground? Or she is playing at the ignorance of the grandparents as they are more likely to believe there are ghosts lurking in the playground after dark.