You know your kids’ endurance better than anyone, so how much they will be up to, after a day of travel, is something only you can judge. But remember, if you have RD planned for the next morning, they will have to be getting up around 7:00 (or maybe earlier, depending on what your plans are for breakfast).
I, too, hate to use a park ticket for a partial day - unless you have it anyway or have an AP. I typically go to DS or one of the other resorts for dinner on arrival day. Although it’s not necessarily my cup of tea, dinner at Chef Mickey might be a good way to kick off the trip for the kids (and you wouldn’t have to “go” anywhere). Riding the mono around the loop, maybe with a stop at one of the other resorts, might be another idea. 1900 Park Fair at the GF gets almost universally high marks from Liners.
If you do have the ticket and it would otherwise go unused, I would say the MK would be (a) much easier, and (b) would certainly be “more Disney” than EP for the kids. CR is a cool restaurant, but unless you manage to get a table right near the aquarium glass, it’s kind of “just another restaurant “ and probably would not be very exciting; I would probably choose Garden Grill instead (for the kids, not necessarily for me).