If you've got the last 2 rows then you will be right next to the snacks, hahaha! The kids can make friends with the FAs. (editing to add: I first read your reply that you've got the last 2 rows but that's not right is it? 2 sets of 2 seats one behind the other is good, though!)
I do recommend if you are on the 6PM flight from SEA to AMS that you get the kids a meal after you get to the airport. You'll want to be there 3 hours ahead of time and will start boarding at 5P. I usually pick up something at the Cafe Flora outlet, Floret - they have an excellent spicy hummus wrap and yes, I get their coconut cake to go...yum! If the plane leaves on time it will be an hour before they start dinner service. IF you are at the back of the plane you may be served last (sometimes they start at the back and move forward but I'm not adept enough to be able to figure out which flights they do that on!!). Definitely take Clif/Kind/etc bars as well.
Be sure to start checking the Delta website every week, Sunday or Monday to see if there are time changes. I booked the SEA-AMS flight last summer for April and it's undergone some big time changes. Right now I'm up to a 5+ hr layover from my flight from Spokane but I'd really just as soon have a long time than a short transit. As I understand it, Delta uploads any changes to their schedule on Saturday, so I make it a practice 3 months out to start checking on Sunday or Monday. Check the flight times and the seat assignments. I doubt they will change the kind of airplane but if they do then your seats may get changed...just best to check everything.
I'd also either bring empty water bottles or get each person a bottle of water at the airport. Have them drink a full bottle before boarding then refill at one of the water fill stations before you board.
What a fun time they will have! I would also sign everyone up for Delta's SkyMiles program!