Religion, teaching, and schools are very, very broad terms so some specifying is in order. To preface, I agree that all children should be exposed to some unified information regarding all religions, but within the current education framework as a whole it does not warrant as much attention as a dedicated class would provide.
Working backwards, school begins with kindergarten, say 5 years old, and for our purposes ends with high school, so at roughly 18 years old. Within that 13 years, society expects that we learn and retain quite a bit. One very important note though, prior to high school, nothing is optional. So to even explore educating elementary children about religion, we must accept that this education would be mandatory and standardized. Because a religious survey course is pretty conceivable at high school age, we should focus on the more interesting topic of education children about a variety of religions. In summary, school will mean elementary aged, public school attending, youths.
Now teaching. Obviously this topic collides head on with those who would object to "indoctrination" because frankly, any teaching that is not exactly their preferred flavor of faith, is a form of indoctrination. To counter this, I propose that we use a very widely accepted genre of teaching as our parameter, history. By accepting that any religious teaching will only be done within the context of history, we can (ideally) avoid the ocean of subjectivity that trying to teach different "faiths" would introduce. Now I recognize that the more philosophical points about religion may not be directly covered in a history class but then, these are elementary schoolers, what sort of philosophy did you expect? Also, the broader philosophical points are not lost just because the teacher doesn't underline it on the board. The exposure to various religious texts and histories raises these points no matter how you frame it, we are simply choosing not to define them so explicitly that we are forced to choose a side. To recap, we are now teaching all elementary schoolers a basic history of world religions. I at least find that a bit more palatable.
So we are left with the essence of the question, "should" we implement this? As a fairly militant athiest, it is hard for me to say that I think we "should" do much of anything to religion besides acknowledge its continued existence and take solace in its inevitable decline. That said, I would truly support the implementation of more teaching about religious history in schools. The content at younger ages is seldom relevant and rarely more than a place holder for a more basic skill being learned. Why not learn to write paragraphs or make a diorama in the context of one of humanity's longest lasting and most controversial institutions?