If your babysitter only accepts payment via a P2P payment app this Re/Code article will help you understand how they work. The article takes a close look at the most popular (except Facebook's new payment feature in messenger) PayPal, Square Cash and Venmo.
My sister and I keep a running tab with each other. She sent a bouquet of flowers for our cousin’s high school graduation; I owe her. I bought our Dad a dual-blade hedge trimmer for Father’s Day; she owes me. She got another cousin the wedding gift that we agreed to split; I owe her. You get the idea.