This came up recently on a mailing list on which I participate, and I think the best answer was this (from a retired Minister).
In summary:
> the bottom line is - if you are Christened in a Christian Church you are “Baptised with water in the name of the Father, the Son and the Holy Spirit.” It is one of the ‘Sacraments’ of the Church on which all major denominations are agreed.
and
> basically, you can choose how you record the event but the generic term is Baptised if you want consistency, regardless of the recipient’s age.
Do read the whole post.