I would just tell them to have fun and be careful if there are smaller ones in there.
Honestly, if kids are small enough that they could get hurt in there, it's their parents' responsibility to watch out for them and not let them in with bigger kids.
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Stacy here!
Enjoying my Complementarian marriage to Mr. Hutch since May 20, 2006
Blessed Mama of Miss H (16), Mr Big J (15), Miss T (14), Mr Little J (11), & Mr A (7)
Missing three I will meet in Heaven (Feb 2012), (Apr 2016) & (Jun 2020)
"Exercise gives you endorphins. Endorphins make you happy. Happy people don't shoot their husbands, they just don't." -Legally Blonde