I found for my DS1 that just Sorbelene cream rubbed on his head worked.

My DS2 has more hair so I used Bicarb Soda and it cleared up really quickly. I just put a little in my hand and added some water to make a paste, then I rubbed it through his hair when I first put him in the bath and then rinsed it out at the end of his bathtime. I did this every day and I noticed an improvement straight away, it cleared up completely in about 4 or 5 days.

Other people swear by olive oil, but I didn't want his hair to go all yuck! (I must be a bit vain )