Right to be concerned - no.
Right to be interested - yes.
To be about as interested in what books they are reading in English is OK.
I’ve taught some aspects of this to secondary pupils, my daughter is to teach parts of a program to y6 pupils.
I’ve never had worries about this and nor does my daughter.
Sex education, health, relationships etc all needs to be taught as some parents are crap at this.
It’s age appropriate - ie no one is going to show 6 YOs condoms, sex positions etc etc.
It’s to do with acceptance. It’s about preventing children becoming bigots - whether it’s yours or others picking on your children - either now or in adult life.
Some LGBT organisations do offer training to staff and some may come in to talk to pupils ( although I suspect they are secondary only) Stonewall are a reputable and mature group and have been at the forefront of training etc. www.stonewall.org.uk/training-courses-and-opportunities
I’m not aware of other types of groups offering training - although I’m sure some ‘Christian ‘ groups may offer advice. If I were a head I’d not touch those groups with a barge pole.
In terms of indoctrination, or turning your child, I think you’ve little to worry about. There’s probably more to worry about Christian indoctrination in some Church schools.
How will you cope if your child/children come out. They often know way before they actually come out and some of the programme gives quiet support to those children, that small but significant minority. Those children who have serious inner worries about themselves and their normality.
I’m sure your rather some work was done in school rather than come home to a child who has taken their own life?
I can understand some concerns but the press have blown a lot of this all out of proportion. Stop reading the Daily Mail?