If its been on a while especially kids suncream which might have a zinc oxide or titanium dioxide its probably after etching the paint. A compound and fine polish by machine or if by hand try autoglym SRP,that should remove it but there a chance the marks could come back.Some come back after time and some don't,it's hit and miss.
If it happens again try get at it with a strong solution of all purpose cleaner as soon as ya can.