How do I tell how many children someone will have in a tarot card reading?

You don’t. You can’t. Nobody can.

no one is able to know the future, even if you manipulate things in order to create situations

You can’t. Free will is involved….and besides, the cards generally only cover a six-month period in the querent’s life, in relation to the particular question.

please don’t dear – leave the things of the Devil to the Devil

Do you actually think that Tarot will tell someone that? There is one time recorded when a fortune teller got it right in the Bible, and the Witch of Endor freaked out when she saw that the King of Israel.Saul, would die.

They will just have to ask that question when you do their reading, and you will have to try and interpret the response. Even if you get your interpretations out of a book, they are still really personal, and depend on placement and context, so it is very situational. It’s entirely possible that the cards can’t or won’t tell you. It’s possible that you can muck it up and not get an answer. Or, whatever forces are at work behind the cards will just not be talking.
I personally don’t think that tarot cards would tell you a specific answer like that.

Repet of your sins, accept the gift of salvation of the Messiah Jesus Christ and believe on Him to be saved.