My 2 1/2 year dd has just decided to cover herself (hair included in Vaseline). I've washed her hair 20 times this afternoon and it still seems as bad, guess I just have to carry on washing unless any of you have any quicker fixes.
Try using a little cornflour, patted gently into the hair, to absorb the vaseline. Shampoo it out (use a clarifying shampoo if you have one), if this doesn't completely remove the vaseline, you may need to wash again. Use warm water to shampoo, if you use cool water it will make the vaseline worse to remove.
Thanks for your tips, it worked beautifully and I can no longer scuplt her hair into a mohican.
Another tip that I was told after I tried yours, for future reference for anybody is to cover hair in talc and then wash with conditioner and then wash with shampoo.