How much money is appropriate to ask for

I’m a nanny to 2 kids. Age 3.5 and 14 months. The mom just told me she was expecting #3 in August. I’m very happy for her and I’m prepared/capable of taking care of 3 kids every day. However, they said eventually they want to sit and talk to me about the “logistics” and money. I currently make $11 an hour 40 hours a week. How much would be appropriate to ask for now that they’re adding another kid? I don’t want to lowball myself or ask for too much.