Select OK (or yes, I can’t remember which one it says). You might get a pop-up message that says something about it needing to be updated. Select that and then select apply to all swatches. Right on top, there will be a toddler box. Open the package with Sims4Studio and then navigate to categories.
If they are no longer active, then you can follow the below steps (note: that this will also work for skin details like freckles, moles, blush, scars but not full body skins). The easiest way to do this is to go back to the creator and see if they updated them. I was recently asked on my tumblr how I enabled custom eyes for toddlers.
