Re: The contents
Some water but it's the high level of dissolved sugar (gluc & fruc from sucrose + invertase) that reduces the availability of the water in the filling to such an extent that it is inimicable for bacteria and mould.
Chocolate shell is virtually water free - add a drop or two of water to some melted chocolate if you want to see why.
Personally I have always found creme eggs sickenly sweet and consume about 1 every couple of years and then remember why I've avoided them for the last 24 months.