I've been doing a lot of reading on this subject lately, because, like you, I'm on the young side (early thirties) to have crumbling teeth. Mine, unlike yours, are cracking vertically and decaying at an astounding rate. I don't eat much sugar or processed food, almost no candy, no soft drinks--I brush, floss, and use flouride. I haven't had children, but we do plan to--and I'm very worried about the effect it will have on my teeth.
Here's what I've read:
1) yes, pregnancies can dramatically affect your teeth--whether or not they are close together, although maybe close together can affect teeth more (cummulative effect)
2) the food you eat is terribly important in determining salivary acidity. Foods that are sugary or starchy or easily broken down into those components are much more likely to cause decay. Common foods like this? Potatoes, bananas, bread and crackers, anything with refined flours. As well, of course, as the obvious things like candy. Chocolate, however, seems to have some protective qualities (I guess minus the sugar...) Foods that are acidic (tomatoes, citrus, etc) also have some poor effects, but not as bad as sugar.
3) food like aged cheese, milk, yogurt, and nuts do not cause carious decay at nearly the same rate. Finishing a starchy meal (like spaghetti with tomato sauce) with aged cheese can mitigate some of the effects.
3) eating is better than continuous snacking. If you have acidic saliva, you are much better served by not eating constantly throughout the day and minimizing the amount of attack on your teeth. Constantly sipping beverages with sugar in them is a big no-no.
4) drinking enough water and getting enough calcium/magnesium is vitally important.
5) finally, make sure you brush and floss and rinse your mouth out after eating--every time.
Whew! It's a lot of stuff, but that's what I've read over and over and over.