Continental is pricing the following with no layover
$1,126.00
Additional Taxes/Fees $183.80
Total Price $1,309.80

This was priced for the first week of October 08. Factoring in a two day layover in NYC the price goes up a bit
1 Adults (age 18 to 64) $1,226.81
Additional Taxes/Fees $194.70
Total Price $1,421.51

Delta was a about $100 more but requires a night over in Atlanta on the outbound, return is direct.

Since you have some KLM miles either Continental or Delta could be parked in your KLM account. Just might want to double ck to make sure the fare basis will accrue miles on KLM, the Continental class is I and X. If they don't give you full miles then best to open accounts for each of you with the airline you choose to fly, cause normally for a fee you could then transfer the miles from your kids account into your own and end up with a nice amount of miles.

SAM