E.B.
I HIT AN 8 YEAR OLD TWO BLOCKS FROM MY HOUSE!The only thing that saved him was his helmet.
get helmets on those kids.
If they want to use your stuff...in your yard it is YOUR rules.
If they do not like it...Send them home. Have a conversation with the parents and lay down the rules.
I bought helmets for ALL the neighborhood kids...and keep a few extra now in my trunk if I see a kid out riding around with out one.
You can be liable if they are in your care, on your things and were to get hit. So you need to make sure everyone involved is safe.
I can not repeat this enough...GET HELMETS ON THEM.
Set a three strikes you go home rule..meaning you catch them three times with it off..They go home for the afternoon.
The parents will either understand and comply or not allow them to come over any more..Either way it is on them to make sure they do the right thing or they are done.