Most kids' weights should pose no problem unless you're on a really lightly rigged small boat. On a moderate sized boat a large adult will impose some shock loads that you'll feel - but again, a well rigged boat can handle all that even though the rig will rattle and shudder a bit.
A variation on the theme: We used to rig the Spinnaker pole up as high as it would go on the mast track and run the halyard through the outboard end. It makes for a better "rope swing" by getting things away from the boat, and reduces the risk of someone who forgot (or was afraid) to let go slamming into the boat on the backswing.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"