J.G.
I was a Navy wife- in fact he was an aircraft mechanic. It was rough at times, but I grew a lot as a person because of it. I'm also the daughter of a sailor, the step-daughter of an Air Force woman (she did it as a single mom and raised 4 very well adjusted kids), and the step-sister of a Navy-then-Airman. When his wife got homesick for Japan, he asked to be restationed there and as soon as a slot opened up they were gone.
Tri-care is great in my personal experience, and I had a baby on it. Just make sure you sign up for Prime though- It doesn't cost anything, you just have to know to do it. My personal experience is that you have the same selection of Doc's as any other plan.
Depoyments come and go, the legnth can vary- navy it was 6 weeks and up. But your neighbors will be military spouses, too, and they will be your family. You will BBQ together, babysit for eachother, and shop eachothers yard sales. It should be mentioned that your DH will earn 30 days paid vacation a year- like any job you have to put in a time-off request, but my ex's were never denied. These days can be taken all at once, or here and there.
Your children are at an excellent age to adjust to the changes. When my ex would deploy, I would put up pictures of his ship and our daughter knew that's where her daddy was (she was 2) We would e-mail back and forth most nights. I've been through the USS Lincoln enough times that I could probably still give a tour of it- and it's been 6 years.
Your DH's career options will be based on his test scores, and if he tests and can't get into what he wants (unlikely if he wants to be a mechanic) he doesn't have to join.
As for his safety- Airforce is about the safest of all the branches, Navy a close second- Based on what his MOS (method of service- ie career) is. I wished durring my entire divorce that I had pushed my ex into the marines instead! All in all the military is a great way to change career paths.
One thing to note- if he wants to be an officer, he has to enter OCS (officer canidate school) by a certain age- this age can vary based on a variety of factors. If he has the time I would recomend that he go Air Guard first, it is (generally) a milder experience and has many of the same benifits.
There are some once in a lifetime experiences that I had as a service member's wife- Watching the fourth of july fireworks from the fight deck of an aircraft carrier is probably my favorite. There were rough times too- but the Navy didn't cause them. Infact the Navy probably made my first marriage last a bit longer. I have friends from those days that I still talk to on occasion.
I wouldn't trade the experience for anything.
edited to add= your DH will likely enlist at a significantly higher pay grade because of his degree. Several things can affect this, having an eagle scout is another. Look into it, recruters don't always ask, and it affects his paygrade and available options.