How necessary is it to wash and prime walls if you're painting it the same exact color?

I am painting my sons room today he has crayon and paint on his walls so i bought stain blocker which i will put over those stains and i bought the same color paint for his bedroom, i was wandering how necessary it is to wash the walls and prime the walls first i don't have much time to do this so i am trying to cut corners and i have never done this before thanks for your help!How necessary is it to wash and prime walls if you're painting it the same exact color?
What type of finish is on the existing paint? If it's satin or semi gloss, the new paint may slide on the wall as you are painting. You should wash it with TSP to degloss and clean, then apply the new paint. If the finish is eggshell or flat, let the stain block dry, then paint those spots. Let them dry and paint the room, and you should be good to go. Hope this helps.How necessary is it to wash and prime walls if you're painting it the same exact color?
in a bedroom washing the walls should be done but not necessary kitchen yes because of grease so you can just paint the walls and it will come out fine