Some excellent prices to New York on when you book with Delta (no CC fees). Example dates 10/8 - 22/8 = £353 (£278 if you have kids under 16 as you can claim back £75 APD).
Family of 4 price (2 adults 2 kids) = £1,263.
Flights are via Paris (CDG) with good flight times. Plenty of sub-£400 fare around these dates.
No need to book with online travel agents and the risks that come with that. You book direct with Delta.
I actually booked an open jaw ticket, flying into New York and out of Los Angeles (£1,627 - 2 adults/2kids), and booked a separate o/w flight from New York to Reno, Nevada for £550 for the 4 of us
Plan is to do Lake Tahoe, Yosemite and down to San Diego, and with no o/w car rental drop off fee from Reno to Los Angeles, it saves us re-tracing our steps and doing mega-car-miles if we flew in/out of Los Angeles.
So we get flights for a 2 centre New York-California trip for around £2,200 for the 4 of us, slap bang in the middle of the school holidays!