@DevilsAdvocate: My question refers to third parties, strangers, attempting to force their beliefs onto young children. That's why I use the word "indoctrinate", they don't just teach about their religion, they attempt to get children to accept their beliefs uncritically.
I don't care what the church thinks, in the UK the age of majority is 18.
Unlike the US, state ("public") schools are actually required by law to teach christianity and to hold an act of collective religious worship (which must be predominately christian) every day. All the school's students are required to take part. There is a little known opt out provision but parents are not informed of it and christian dominated schools have been known to deny it exists or even refuse to comply.