It's tempting to buy the kids in your care a little gift, an ice cream cone, or a ride on a carousel at the mall from your own pocket sometimes when you are working as a nanny. But, it's a bad habit to get into and parents don't (or shouldn’t) expect you to do that.
Parents should provide petty cash for you to use when out with the kids and their friends. It's also useful when parents get a credit card with a limit on it so you can easily buy groceries or have it in case of an emergency.
In return, you need to keep receipts for all purchases made with their money while working. Typical costs you may need petty cash or a credit card include tolls and parking, food, and entertainment.
Don’t get in competition of trying to buy the best birthday gift for your charges because children don't really care how big a gift they get from you. Kids don’t need expensive gifts from you. In fact, kids don’t even really care how big their house is, if they eat lunch at home or at the pizzeria, or how much their clothing or toys cost. They won’t remember you bought them an ice cream cone with your own money but they will remember that you gave them your undivided attention, you listened to them, played with them, and appreciated them.
Before pulling out your own wallet to pay for outings with the kids remember professional boundaries -- you are working as a nanny and it isn’t your place to spend your personal money on the kids.