Apologies for the tone, which is unintentional. Yes, I do come across more strongly than I intend; others have pointed that out. I'm trying. But, well, sorry, meanwhile. I don't mean to be aggressive or defensive.
Thing is, I just think, if you're to take your subject at all seriously, you should judge other people's religious beliefs when those beliefs are demonstrably and obviously silly.
A chemistry teacher who told her pupils about phlogiston but didn't point out the truth about it (no such thing) ... or a physics teacher who was asked about teleology and Aristotelian final causes as explanatory of the motion of the planets and didn't point out the flaws in such notions ... such teachers would rightly be held to be unserious.
Of course you teach about transubstantiation. But do you teach about its background in Aristotelian/Thomist metaphysics of substantial forms etc., and point out no-one (outside the Vatican perhaps) thinks any of that makes sense, or has done since the seventeenth century?
[Here's something Anthony Kenny (distinguished philosopher, famous ex-Jesuit) had to say: "... the metaphysics we were taught appeared to save the coherence of transubstantiation only at the cost of calling in question our knowledge of every material object. For all I could tell, my typewriter might be Benjamin Disraeli transubstantiated, since all I could see were mere accidents ..." (Kenny, A Path from Rome, P.72) Kenny surely is right about this.]
I don't say you shouldn't tell children some people believe in transubstantiation and some don't. That's fine. Just not enough.
--Because you can't really be thought of as engaging seriously in your pedagogy unless you also tell your pupils some people think transubstantiation is absolute nonsense ... and why, ... and where they got such a ridiculous belief from. (And, yes, that it's very much part of acceptable contemporary thought that it îs ridiculous ... and why this should be so.) Otherwise, yes, you're simply gilding the lily and selling your pupils short.
Do you tell children why most serious people think transubstantiation, Divine Command Theory, the efficacy of prayer, and all the rest is such a load of tosh? Does your subject include such balance? If not, it's not to be taken seriously and starts to look - yes - like disguised indoctrination.
(Think of the chemistry teacher: "Some people believe in phlogiston. Others don't." Is that a serious approach to chemistry if it stops there?)