All of the major cruise lines have kids' programs. My grandchildren have seemed to enjoy all of those they've been in, and we practically had to pry one grandson out of Club HAL.
One family we met on a cruise had a particularly bright idea: they brought a 6-inch rubber ball with them. As soon as they got on the ship and got to their staterooms, Dad and son made for the pool and started playing catch. Within minutes another boy was watching somewhat enviously. Dad then tossed the ball to him, and once he got it back, to his son. After that they started going three-way. In very little time Dad was out of the pool and the boys were having a ball. When they later met in the kids' club, they already had a friend. Your boys will have the advantage of having each other, but a new friend on board always helps.
One other thing: the European lines, like Costa and MSC, run their kids' programs differently. They tend to not start until later in the day, sometimes as late as 3 p.m., but they also will keep the kids through supper and the evening, until midnight or later.
I think anytime you can take your children to another country is always a great idea. It helps them to grow and learn, which is a very good thing. We traveled as much as possible with our children and while we couldn't afford to take them to Europe, we did take them to Canada and Mexico on several occasions. And I don't mean just to the border towns, I mean well into the countries. Because of that, they are more tolerant of others and have a great hankering to travel wherever and whenever they can.
As for what cruise line to go with, that really is a personal choice. As I always say; what one person loves, another will hate. Personally, we found Disney to be wonderful for kids. Their children's programs and entertainment are great. However, the two things we did not find to our liking was the food in the main dining room was okay, but not as good as it should be given the price you pay. And that's the second thing we didn't like; their pricing is considerably more than others.
The newer larger ships are all full of amenities for children, especially the new RCCL ships. So, I would definitely suggest considering all of your options.
Traveling to Europe with a family is a fairly hefty financial investment, so it really depends on your budget, your lifestyle, and the itinerary. There are some amazing places to see, but if you're traveling during tourist season, make sure to pack your patience. Young children don't do lines well and at any major attraction, lines can be exceedingly long, not to mention hot, if you're going during Summer. So, plan accordingly.
Definitely talk to your agent - hopefully, they've been on the cruise lines and ships going to the area you're considering, as well as to the ports, so they can provide some very helpful information that will help with your plans.
But I commend you for wanting to take your children on such a wonderful experience. I hope you'll come back on this forum and let us know what you decided to do and how everything went, as I'm sure others would be very interested to hear all about it.
__________________ Travel Agent/Cruise Specialist w/15 yrs exp and 50 Cruises on 12 different cruise lines in many parts of the world! VIETNAM VETERAN OWNED & OPERATED. Certified Accessible Travel Advocate. Specializing in unsurpassed personal service to insure you have a hassle-free vacation!