"As a kid in Catholic school, I grew up learning a lot about Mary."
We had nearly identical experiences.
"Though I admired Mary’s pastel prettiness, I always thought the Immaculate Heart pictures were kind of creepy. After all, no woman I knew had a transparent chest or an exposed heart. I always found that image foreign, off-putting, and bizarre."
I also thought the exact same thing.
"Having lost two pregnancies before Matthew was born"
I'm sorry to hear about your two previous unfortunate events, but am glad that you finally received a healthy baby in the end.
"Matthew is out of me now, in the wide open world"
Up until this point, I thought this article was outstanding. The above snippet is a good way of looking at it.
"I thought again of Mary’s Immaculate Heart. For the first time those pictures of her open chest began to make sense."
Those pictures of her open heart do make sense, but not for the reason why you suggest. Pictures like these do indeed have a purpose and that is psychological power on behalf of the church over their flock. This is PRECISELY why both you and I found them to be creepy. And by the way it sounds, Matthew will one day be subjected to this as well.
In fact, if you look at other propaganda machines such as our own US Military and their flags, they have similar concepts such as the Army has weapons piercing through where a human should be in the breastplate, the Marines have an anchor piercing through the planet, the Navy has an anchor which at first glance appears to be piercing through an eagle (though the eagle is standing on it) and the Air Force has both thunder and lightning bolts piercing through a set of wings that are a sort of an effigy of the eagle sitting above them.
None of that even comes close to more modern versions such as this special forces flag:
So when you and I were little kids sitting in Church staring at the pictures/statues with these bizarre (which is a kind word) images, we were being psychologically influenced (in a negative way) while our parents were blind to the reality (because they had already been brainwashed via the constant repetition of seeing those images themselves).
Ask yourself this: Would you let Matthew watch a scene from an R rated horror movie when he is 5-8 years old with some character that walks around with a beating heart covered in thorns and blades pierced through it??!? Of course you wouldn't. Why? Because it would be psychologically traumatic for him. Yet if it is in church, then it is somehow "magically" completely fine. It is insanity.
"I’m sure that she, too, worried about her baby’s health."
If you are to believe the Catholic version of Mary where she was a virgin and gave birth to Jesus via a message from an angel (despite the fact that via the Gospel writers own accounts that it was literally IMPOSSIBLE for Jesus to have been born due to conflict in dates), then why would she be concerned about her baby's health? If my child were the Son of God, I don't think I'd be overly concerned.
"Losing the teenage Jesus in the temple must have been terrifying"
This was one of Jesus' sins in the Bible (despite Catholicism teaching otherwise). I agree that it certainly wasn't "Honoring thy mother and thy father."
"terrifying, while watching her adult son embark on his dangerous ministry surely took massive reserves of maternal courage."
Once again... he was the Son of God walking on water... if anything she had easy as a mother knowing that he was protected by the best protector imaginable.
"Everything else, of course, pales in comparison to the crucifixion. How she endured her son’s torture and death I will never know. I do know that it was love that kept her rooted there at the foot of the cross, even as her heart was breaking."
And what about Mary Magdalene? She was more important than Mary Jesus' mother according to the Bible.
Feel free to see how that is the case here (I'll also include it as a reply to this post below):
"But if asked, I know she’d choose it all again"
She gave birth to the Son of God and now gets worshipped as a demi-god... of course she'd do it again.
"One thing I’m learning is that the drive to love is more than mere human instinct. Thinking about it from a spiritual angle, loving another person is a chance to align ourselves with God and to transcend our own cautious plans for our lives."
So are you saying that Buddhists don't know how to love? Are you saying that mentally ill children who can't possibly understand God the way you do don't know how to love? Are you saying that the Ancient Egyptians didn't know how to love? Are you saying that the Native Americans (who never heard about Jesus for around 1,500 years after Jesus died) didn't know how to love? Are you saying that atheists (such as the two biggest charity donors on the planet Gates/Buffett) don't know how to love?
Love is an innate human instinct.
"Thanks to the experience of raising my little boy, Mary’s open chest is no longer off-putting to me."
It's not off-putting to you because you have been indoctrinated to it via repetition and the cycle will continue with Matthew.
"I’ll be OK, too, I realize as my heart darts away from me on determined legs, ready to take on the world."
As a friendly piece of advice from someone with higher education degrees in Communication with an emphasis on children, have your son watch Sesame Street as kids who watch it tend to do much better in school, both academically and in terms of relating with other children.
Best of luck to you and your family!