Possibly. A property owner who tries to impose limits on families with children may be violating fair-housing laws that protect familial status.
The U.S. Department of Housing and Urban Development says an occupancy policy of two people per bedroom can be reasonable, but other factors should be considered, including the size and number of bedrooms, the age of the children, and the configuration of the unit.
You should ensure that your occupancy policy is consistent and applies to all occupants and rental applicants. For example, you can’t refuse to rent to one family because they have children or demand that a tenant with a baby on the way move to a larger unit.