There are 3 things that I don't allow others to touch
1- My Guitars
2- My Bike
3- My Wife
In that order and Mrs Tiger knows this is the priority (she is 3rd, cause she can speak for herself, before I need toget involved)
We love kids and I will give a ride to any and all, with their parents permission, as long as their feet touch the footrests. My one pet peeve is if someone puts their hands on my bike's tank, my bikes are usually polished, especialy the Triumph Sprint, even family or friends get kaked out for pawing on my tank, not so fussy on my KTM though, she isn't a "Pavement Princess" and deserves her dirt honestly

My brother-in-law is a laat lametjie and one Sunday he climbed on my Yammie XS Eleven Special just after I had stopped ( at the time he was 3-4yrs old). The bike fell over on him, and I rushed to pick up that big lump of metal off him, after checking he was OK, I gave him a moer of a hiding in front of his parents - never had any problems again, even now he is 28 he still askes before getting on my bike

My biggest concern is someone destabilising the bike while a kid is on it if I am not around to supervise, the parents will quickly blame you or bugger off without taking responsibility for damage to the bike or kid. To me it is like someone climbing into my car while I am away to check how it feels.