Quote Originally Posted by veti View Post
*Untested answer, save before attempting*.

If you have stored anything in the children's bedroom/alchemy lab area, take it out first. No telling what might happen to it.

Then: close doors, go outside the house, and enter the following console commands:

prid e4ef9
disable
prid xx004274
enable

... where 'xx' is the position of Hearthfires in your load order, expressed as a hex number. (Base game is 00. Hearthfires is probably 03?)

This assumes you haven't previously installed the alchemy lab. If you have, then follow the same procedure but replace the first line with:

prid e4ec8

This should install the room in your house. I don't know if there's anything else you need to do before you can invite a kid to move in, but if this works it should be worth a try.
Tried this, didn't work. It says that item parameter cannot be found.