HI, Jennifer -
I'd be nervous, too, but they'll be just fine. I would make up a big master schedule that includes the what/where/when of the kids' activities. Or, you may do a more "journally" type that details what is on the schedule for each day. That way, your hubby will have a cheat sheet and time schedule for every single day he's without you. When I'm away from my kids, I also help my husband by making sure I have all the staples for the kids' favorite and easy to fix meals in the house, and that all laundry is completely ready to go. I even put the outfits together for him so that the kids don't look too goofy in the combinations Daddy might come up with - not crititicizing - he tries! I'm sure you can be accessible by cell phone for those last minute questions, so don't worry. Daddy and the kids will muddle through, strengthen their bonds, and learn to appreciate Mama even more!
Have a wonderful time.