Offering payment to a babysitter who's a friend

I used to babysit my nieces sometimes when their parents went on a night out.

Bro: “Wanna be paid for that.”
Me: “Nah.”
Bro: What then do you you want?"
Me: “A beer and some salt snack.”
Bro: “Deal.”

(side note, I just gone alco legal at that time)

You could also opt to do a favor for them. “How about I sit your kids for free next time?” Or watch their pets, or take them to the grocery.

If you take my cat to the grocery, no one will make it out alive.