How much do it cost for two people to come to the u.s?do they need a visa or passport to come to the states.what is the cost for both people?woman and child.

Do you know this woman and child? Have you met in real life?

Cost would include plane fares, hotel charges, food, an apartment. They should go to the embassy in Ghana.

The chance for citizen of Ghana to get visitor's visa to US is equivalent to zero. Please read: https://www.askmehelpdesk.com/visas-passports/ghana-romance-scams-442160.html

I would recommend you go visit them in Ghana.

Yes, first 99.9999 percent of people who happen to be there on dating sites or spam email are all frauds. And unless you talked to them on web cam, most likely they are not even who they say they are. Several people will use the ID of one nice looking person.
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So have you meet them before in person.
HOW did you find out about them?

Have they asked for money, and if so how much

Next if you are not listening to this, at least on the airline ticket make it a prepaid ticket that they can not cash in and only you can get the refund if not used.