Family Size is messed up

You can have a Family Size of 2,

then you can mark down that 2 members of your family are between the ages of 4-17. which is fine. 

then you can mark down that you have a child under the age of three. and this is not fine. 

that makes your family size actually 3. unless we aren't counting children under the age of three part of the family. I am okay with this. 