I converted 7 of the Sims 2 beds into toddler beds for our Sims 4 Toddlers. I found it is not so easy to do the beds as you have to be sure they do not go through the floors nor can they be close to the walls. I did check to be sure they could be placed without having to use the bb.moveobjects cheat. I was only going to upload 6 but I finally got the classical bed to work, it was a challenge.
The mattress is separate and may be placed without using a cheat. I have 59 textures for the mattress in the same design used by Sims 2. I pulled all bedding for an EA bed to use on this mattress. All frames have the EA textures also. Feel free to add any beddings you might have from Sims 2. I do not use the small little section of the bedding I use the full bed texture.
Issues: The only issue I know of is that you have to move the mattress and frame separately. The extra benefit is you may recolor the frame and bedding separately.