I was never Christened, thankfully, nor were my children. My ex's second wife tried to get them Christened when she Christened their daughter but I was not having that.

Thats bloody daft

Doing stuff like this just gives them validity to their religious ways and beliefs.
Doing such just gives weight that their ways mean something, They don't.
The best thing is to just walk away, and say no more about it.

As a bit of fun it's great idea. As a serious issue what's the point?

Personally this seems silly to me. Something akin to giving all your present back to Santa.
Church is foremost a social outlet for us. Even an adult Santa for some and charades for others.
We can grow. but the past is alway, just the past.