Your classic go-tos are: nail polish remover and hairspray (I'd go with the former first). If you wanted a product then, if in doubt, I always reach for Dr Beckmann's and the their Stain Devils range has a pen and ink remover that also works crayons (although that makes it sound suspiciously generalised) - with young kids in the house I'd have that and the trust carpet stainer remover to hand (well, I keep the latter in easy reach generally).