I think, unless you are very wealthy, when you have 4 children, you wave goodbye to all inclusive for two weeks.... It just gets prohibitively expensive.
We have 4 children, 16, 14, 11 and 8. Did two weeks in France (just returned yesterday). 380 for crossing (motorhome plus bike trailer so more expensive). 690 for camping for the first week but included theme park tickets for the whole week, so meant we spent nothing on excursions. 320 for second week, on a beach and pool with slides, so again no other trips out. Did pay a bit in fuel and tolls.
Went to McDonald's twice on travelling days and had a portion of chips out once. Otherwise everything came from the supermarket and so probably spent less than we would at home.
Probably all in, still comes to 2k and it is hard work, but if you have 4 children, pretty much everything is. It is still unachievable for many. My sister goes to a great campsite in the Dordogne on a river (swim in the river rather than a pool) and they pay 25 euro a night. You can pay a bit towards your crossing with clubcard vouchers.
You do have to have camping kit and we have built it up over the years. I get something new each year. This year I upgraded the blow up mattresses to memory foam pads.... The luxury!