Scubamum
The best opportunity your kids will have to gain employment in the industry will be to arrange it when they do their top two courses, so when they go to do their Divemaster, they need to speak to the shop about getting work after they have competed it, and get an assured offer of work, not just a vague "we'll sort something out".
As other people have posted, there are a lot of DMs in the world and they work for cheap. My Girfriend used to get $1 per tank! The least popular the resort the less DMs you'll have there, the more chance of work.
Lastly, the IDC... the Instructor Developement Course costs a fair bit, you're looking about $2,000 ish dollars. It's a big spend. Before they chose the IDC centre, try and specify that they are looking to stay and work after it, again this is the best chance to get their foot on the ladder. From there, experience and languages will get them the rest of the way.
There are other companies - just google them, people like Dressel Divers, or Prodive that have centres in the big All Inclusive resorts that (in Dressel's case) will take you through DM and into Instructor level with the sole aim on employing you afterwards.
Once you're in as a Dressel diver *and it's not for everyone - they're busy, hard working shops... then you have the opportunity to work in their other operations around the world.
This is more like being a rep in a big resort and may not fit into the free travelling idea they may have, but it's a pretty good career and a good name to have on your diving CV.
...again, hope this helps!