If your sim is still a teen and sneaking around the house then you can enroll him/her to Bording school then take them out after the first day .
But if your sim has grown up and still sneaking around you could either move him/her to a different house (which i found didn't work ) or follow these steps .
1: press ctrl+SHIFT+c at the same time on your key bored.(which will make a box on top of the screen appear.)
2:in the box type in testingcheatsenabled true (No capitals ,1 space between enabled and true ) then press enter .
3:find the sim that you want to stop sneaking and click shift on your keyboard while clicking on the sim .
4:An option should appear saying "Edit sim in creator sim" Which will make you go back to creator sim (don't worrie all the memory is still there !)
then change your sim from young adult /Elder ect to a teen then click the tick .
5:now your sim is a teen she/he you can enroll your sim to bording school ,after the first day take him/her out and repeat steps 4 and 5 but instead of changing your sim into a teen change it back it to an adult
SIMPLE !:)
Hope this helpt