How do I go about asking my son's father mom for stuff for the baby?

My son's father wasn't in the picture until now..it took me two messages to him and his mom, for him to show up. Now we are trying to work things out.. His mom was the first to message me and tell me that if their was anything I needed for the baby I could ask her for it.

But Idk how to ask her since she isn't responsible for all this, but at the same time their are a few things my son needs.

The son's father is supposed to give me money for my son every month, we have come up with the amount ourself. But he hasn't said when he'll start paying.

How do I go about asking his mom for pampers, clothes until her son starts to pay? I'm not really sure on how to word it.

Thanks!