When do they want to go? For how long? How old are the children? Do they want to stay on site?
Park Passes:
Paramount has great prices on their park passes; some of them come with breakfast vouchers. If their trip is still some time away, they could buy one ticket at a time to spread the cost out.
Meals:
They can join connections to buy the meal vouchers. Counter service meals will keep the food budget low. Vouchers will allow them to pay for their meals before the trip.
Resort:
Keep checking mousesavers. They may be able to get a great rate at one of the on site resorts. If they stay on site, they won't have to rent a car.
If the cost of staying onsite is to high, they should be able to get a great deal at a hotel close to WDW.