You should be able to go in build mode, either through manage worlds or directly when playing with the family.
As the toddlers came after the expansion it's understandable that the beds for toddlers are missing.
I do not work for EA
You can't normally go into build mode when you're renting a cabin but you can use bb.enablefreebuild to do this and then place as many toddler items as you need.
June 2018 - last edited June 2018
Sorry to necro, but no non-cheat answer was given.
Child to elder can click on toddler bed and put in invintory and take it with them.
Edit:you can also buy toddler beds from the supply hut, though there are no toddler potties, have to go in diapers? Time to manage the camp world too bad I'm already in the cabin!