The Crayola website says that you use WD40 to get Silly Putty and clay out of carpet… but they don’t say anything about hair. jdimbert thinks that she heard advice to use lighter fluid, but I’d like some corroboration before we go there.
I’m no parent, but if the silly putty is not stuck too close to the scalp the easiest thing to do would be to apply ice. As the silly putty’s temperature is reduced it will become less sticky. You could probably peel it right off.
I have no idea how to get it out of hair, but I WOULD advise you to take a picture of this before you try anything else. Just for blackmail purposes. Trust me, it’ll come in handy someday.
Kniz, presumably you found the same website I did, putting “silly putty remove hair” into Google, but upon further perusal, I see that the “Silly Putty” it’s talking about is homemade, with Elmer’s glue and starch.