Context, context, context.

You could explain to your sons - wherever the topic comes up - that the Old Testament focuses on sacrifice, sacrifice of valuable animals (but as you will recall, only the very most valuable was acceptable) and in this context, sacrifice of a very valuable sexual function.

I cannot see that these early Semites were idiots. They certainly were unreliable as the story unfolds, but they knew only too well what the foreskin was for. As happens in our day, it was as a concession somewhat easier for them to do this to their children instead of having to make the sacrifice personally, so an element of denial clearly comes into it. Even then, it became ridiculously ritualised when the Bible makes no such expectation whatsoever.

Just why did God - who created Adam "perfect" in detail including the foreskin - then require circumcision? I would say it directly relates to the prevailing religious cultures mentioned here - the fertility rites which involved amongst other things, semen and sometimes blood. (You clearly realise the importance of blood in the Old Testament and will recall that emitting semen was also a cause for becoming "unclean".) A circumcised man would be less than acceptable in such rites, because an important part was missing, so this provided just one little barrier for their participation. Of course, it did not entirely stop them, but it was a nagging reminder that they really were "set apart" and should not be participating. As with the Egyptian priests who also were apparently circumcised (at puberty, of course, as part of their initiation).

When you explain these things, it follows that since we as Christians are neither required nor permitted to perform sacrifices (which makes Roman Catholicism the more suspect), then circumcision falls in the same category - if it has any religious significance (even tangential), circumcision and anyone recommending it, repudiates Christ.

Paul's writings make this only too clear, so there is no reason to shy away from such references as long as people understand them. "Circumcision of the heart" does not at all connect with the act of cutting, but the sacrifice of something of personal value - autonomy - in deference to God.