I want to put lights and pictures in my girl’s room. 12 & 7 yrs old.

If the walls are smooth enough, use command hooks or strips. They really do work, just get the ones that take more weight than what you are hanging to make sure that what you put up is secure. Put them up as the package tells you to and leave them up with out hanging anything on them for the time they have in the directions. Didn't wait once and the speaker I hung on it fell and almost broke the glass shelf on the entertainment center.

hook and loop tape removable adhesive.

Command hooks and dollar store picture frames which you can paint! Let the girls make their own art and place in the frames.

You could give each of your girls a bulletin board to hang their art work, school projects, etc.

Command picture hangers will hang stuff without making holes. I have glow-in-the -dark stars that stick on the ceing, and another option is mini lights on a string.