Hiya
The first thing that strikes me from that is £400 per month on food. That does seem excessively high an estimate, that said, maybe you're including quite a substatntial proportion of that to be eating out? if not, then for 2 adults, and 2 small children, that's a lot of food you're going to be munching on !
Next - Insurance's. Unless you've included it in some of the figures? Content's insurance, car insurance, health insurance, travel insurance (for when you're out of the country on holidays etc) any life insurances, loan protection insurances, mobile phone insurance, laptop insurance etc. Added together they can be a significant amount.
Utilities - Main ones are of course Electricity and Water. Gas if the place you move to has it, I see you've included internet in there as well. Budget for a phone line rental, Sky/Virgin TV will you go SKy+ or Sky HD?, 2 mobile phones?
As already mentioned, council tax, any housing maintenance fees for upkeep of the property (could be a landlords responsibility) car MOT & road tax and running expenses. Petrol is hard to calculate becuase needs can vary, insurance depends on the car you get.
Great that you've included 'emergencies' - you need to set a solid figure for that though. Many people will set a percentage of their disposable income to go straight into a savings fund, as a direct debit as soon as they get paid - so coul dbe worth looking into that.
For now I think that's mainly it, but of course it can still vary depending on other factors like how much entertainment or gym fees or sports recreation etc etc you do.
Hope the above helps a bit!
Cheers! DtM! West London & Slough UK!