Family Sharing can only accommodate 6 people total, which includes the Organizer. If you have more than 6 there isn't an ideal solution. For some of the youngest they may have to share an account until they really need their own, by which time hopefully some of the oldest ones can leave the Family to be independent. Either that or have another responsible person set up a second Family Group and take on some of the new children. Note that you can only belong to one group at a time though, and there is a limit to the number of times per year that you can switch to another group.
You are welcome to provide feedback to Apple about this but I have seen posts like yours regularly for the past decade or so and I would guess Apple is aware of this issue. It probably isn't just up to Apple to decide what makes a family since it is the media companies and other content owners who want to place limits on sharing. Actually 6 is fairly large for a nuclear family in the 21st century. It used to be there was no Family Sharing at all and everybody had to buy their own copy of everything, so Family Sharing was a big step forward. ;-)
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