I know that the adults and students sleep in beds. The babies sleep in cribs. Do the toddlers need a specific bed? Right now they just sleep wherever on the floors, and no one has yelled at me to get them proper beds. Do I need to?
Children have two states: Baby, and Child. Each state lasts a year. Babies use cribs, as you said. Children on up can use beds.
I found out through observing my married couple, that Beds will get used on a first-come, first-serve basis. Since only a single person can use each bed, you would theoretically need at least three beds.
I can't find anything that says kids, or even spouses need beds. There may not be any detriment to not giving them a bed, but each one increases rent of the apartment, so it might be a good thing to add it, if the space and tenant wealth can support it.