May 2018
If you want to play more than two sims at the same time you will need to buy a third and/or fourth slot with simcash.
If you don't have an open slot you will need to retire an active sim first to open up a slot. If you have an open slot simply click on your family picture in your house. While in the picture, click on the sim you want to promote into a playable slot.
You do have to wait until your kids grow up into adults. In most cases this takes about 6 days.
May 2018
If you want to play more than two sims at the same time you will need to buy a third and/or fourth slot with simcash.
If you don't have an open slot you will need to retire an active sim first to open up a slot. If you have an open slot simply click on your family picture in your house. While in the picture, click on the sim you want to promote into a playable slot.
You do have to wait until your kids grow up into adults. In most cases this takes about 6 days.