We went in March, when the dc were 5 and nearly 3. It was fantastic! Definitely worth going when they are little.
We stayed in a Disney Hotel (Sequoia Lodge) for 4 nights BnB, 5 day park entry. I booked it when they had their 'two nights free' offer on. For two adults and two children in the main lodge (you pay extra to be next to the lake) it cost £670, which I thought was brilliant value.
We drove from Wales (1000 miles round trip) and stayed in two hotels as stop overs, and got the ferry...total cost of petrol, two stopovers and ferry was around £350.
So, around £1000 for everything, including travel. We spent another £1000 as spending money over the five days...but we didn't really budget, we bought what meals and gifts we wanted, did a day trip into Paris etc etc. I reckon we could have done it with about half the spending money, if we'd been more careful.
So, in total, cost around £2k. It's expensive...but for what the adults kids get out of it, also very worth it! I would go again tomorrow!