The secularization of teaching about the facts (just the facts, no preaching allowed) on religion to young children would fall within the standards supposedly in use for teaching of Comparative Religion in High School. No preaching is allowed if those standards are appropriate and fall within the boundaries of legal separation of church and state (the curriculum, of course, would be different based on the younger age level).

However, if those standards are flawed, and teachers (or legislators) try to abuse them to promote a particular religion (in America, that would likely be to promote Protestant Christianity in most school districts), you'd have the problem that you fear.

Of note, the current American political fad is to try to create an ecumenical Judeo-Christian-Islamic God of all ... something intellectually meaningless, but nevertheless used (with disregard for Hinduism and all non-monotheistic religions, like Buddhism).

Those who respect the right to believe and disbelieve as one chooses should, at some point, be able to create public tolerance campaigns which promote the rights represented in the first amendment.

However, that being said, the secular education of young children, on religion, should provide the intellectual tools which diminish the deleterious impacts of single-mindset indoctrination. Most kids (in America) are not educated in that way and many of them grow up with a life-long feeling of intolerance towards alternative religions, disbelievers, doubters, and others distanced from faith.

As for the single-mindset indoctrination crowd, the first amendment protects their right to push their religion, at home, and in churches-synagogues-mosques-tents-temples-wherever. Ideally, curriculum on religious education should be made part of private schools (and home schooling) based on state standards for education.

As for regulation of behavior, that would continue as it does now, with parents and school teachers and other child role models continuing as before.

The only difference within the secular education model for teaching religion as a mandatory part of school curriculum is that the children would have the tools with which to make their own determination as to the efficacy, or lack thereof, of the particular religious paradigm being offered them at their home (and religious institution, if applicable).

Keep in mind, with school curriculum respecting logic and reason, the facts on disbelief and doubt and open-minded search for verity would be part of the curriculum, and would respect those of us who have chosen to approach religion skeptically (3 cheers for us).