Which has better in-flight entertainment for a seven-year-old and a four-year-old?
KLM or Emirates?
Emirates, hands down. Emirates ICE has a huge TV in every seat with 600+ channels including a big kids section, and they only have new planes. On KLM, if you end up on their ancient MD-11s, you'll be squinting at a screen the size of a postage stamp in the front of the cabin (and that's in business class!).
In general, Emirates is the better airline in every possible dimension: better seating, larger screens, better food, better service, better hub airport, etc.