I asked my sister who's a retired teacher in Canada. Her response is below. Hth.
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In BC the minimum wage is about to go up to $10/hour and about time too.
You are not supposed to pay less than that between strangers.
However, between friends and neighbours, on Salt Spring Island, the sitter might well think $10 too much and be a bit embarrassed to accept it.
However, at the school, teenager offspring of parents attending a parents meeting get $2.50 per child (that is, however many little ones there are to supervise, and however many supervisors there may be, the parents of little ones put $2.50 into the kitty per child they are dropping off, and the available teen crew divide the total evenly between themselves. (That way it's a bonanza if you're alone and the load is heavy, but if there's lots of you to have fun with, you may have to divide $2.50 (and the kid) between you, which the teens seem to feel is Just & Right. Incidentally, if no teens turn up (a rare event - it can be a chance to do your homework if there are enough little ones to play together on the carpet with all the goodies in the Pre-School classroom), an adult does it - for the same rate, accepted as compensation for volunteering to miss the meeting - a few do usually take it in turns, not to miss the whole meeting.
My own guess would be that $10 for 3.30-5.00 would be just fine to offer a 16 year old - certainly where I am.
I'd suggest this be offered, and carefully watch the body language and facial expression to check that it's not too cheap; if the 16 year-old shows any sign of disappointment, you can say that's the rate on a trial basis (give an end date - might be after 3 times) after which you can both sit down together to discuss the rate again.
"You get what you're willing to pay for" has long been a standard piece of cliché advice, but not at all true in my case (I mean if you were paying me; I'd MUCH rather not be paid at all, so I can say thanks but no thanks next time, if I didn't honestly enjoy myself the first time! But I'm 62, not 16...). It's true that a teenager will stick at a plum job that's the envy of her peers, and really try to make a go of it. But more than anything else, it's probably all going to depend on how the child takes to the teen, and vice versa. You want the situation to feel OK, and the relationship to have a hope of developing into a mutually satisfying one.
I'd say don't ask back anyone who complains about your child, or anyone your child complains about, if there's any lingering tension. (At the school, pre-schoolers tend to adore teenagers, and vice versa. But one-to-one that might be different.)
I'm vaguely aware that if you are employing anyone, including for babysitting, there's a regulation I'm not up to date on, about minimum hours per week (4, the last time I noticed) - that drives both parties crazy.
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