1) get 60 in sneak by level 10
2) choose the "mr. sandman" perk (available at level 10)
3) go to andale , and wait for the children to go to sleep
4) sneak up on the sleeping child and use the "murder" option
5) since kids cannot be killed , you can repeat step 4 for unlimited sandman kills and EXP. that comes with it.
6) repeat until you reach level 20.


NOTE:

the children (and parents) go to sleep at midnight and wake up at 5 a.m. it is recommended to have auto-save enabled , since it is possible for the game to glitch while utilizing this method and sending you to "never-never land" unable to return. The auto-save is handy while waiting the 19 hours for the kids to return to bed.

It is possible after waiting the 19 hours , that the child dosen't return to bed , if this happens , leave the house go to the neighbour's and repeat on the other child.

although it's "unlimited EXP." the cap level is 20 after that no more exp. will be gained but the sandman kills will still stack up.

no karma will be gained or loss , since the murder does not register.

it is a very quick way to get to level 20 , but you will not get the ammo , weapons and caps that you would normally gain from reaching level 20 by "legit" means.