Can you try using 'grownup' shampoo and repeating the washing/rinsing process until it feels like it's gone? Just be careful (as you know) not to get this mixture into their eyes as the vapours can be strong. I did this after finding my youngest had rubbed an entire large tub of sudocrem into her hair, face, sheets, walls and I used my own shampoo which I believe is much stronger/soapier than her organic, sodium laurl sulfate-free baby shampoo! Good luck!