Someone got an unexpected sum of money.
He wants to distribute it to his children all of them are married with children (one with 7 one with three and one with 2 children)
Only one of the grandchildren is bas mitzvah.
What would the best way to figure out the amount to be given to each family?
If the money that you are distributing is considered tzedakah money then it should only be given to those children that would be allowed to receive such monies. However if it isn’t tzedakah money, then you can really distribute it in any way that you see fit. I don’t know your children’s families, so I can only give you general ideas, and you can apply them as you see fit. On one hand you have to make sure that you are not going to cause jealousy among your children, and that they will not feel that they are not liked as much etc. Aside from that, if some of them are studying torah, they should be given special consideration, because it is a big zechus to support torah learning, and this will serve you very well in this world and in olam haba. You may also want to distribute it according to needs of each family. You might want to seperate some of the money for the grandchildrens weddings etc. All of this will depend on the specifics of your family and the families of your children.