I have a grand c-max and we are a family of 5. We use the extra two seats now and then, what's handy is that all the rear seats are independant, you can have a 2 + 2 config leaving a little walkway through the middle row, or 3 + 1 which we use when we have an extra on the school run. It drives well and isn't outrageously large, no problems parking at the supermarket. But the boot with the extra seats up is very small, enough for some shopping but not enough for a holiday to France. I think the same is the case for most of mid-sized family 7 seaters. If you need extra seats now and then for a short run with some extra kiddies (or grandparents in the middle row and kiddies in the back), they are fine. If you need to regularly seat 7 and luggage, then not so good. If that had been my need I would have selected an s-max for sure.

I might be wrong but I understand the OP has two children and would only need 7 seats when relatives/ friends visit, so the need for 7 seats AND boot at the same time isn't so pressing.

Don't know the budget but I would look at Vauxhall Zafira, Toyota Verso, Mazda 5 (six seats really), Ford S Max, VW Touran, Citroen Grand Picasso, Peugeot 5008 and throw in a Mitsubishi Grandis too.

Of those, the Picassso/ 5008, Zafira, Grandis and S Max seem to have the largest boots with 5 seats in place. I look at some smaller MPVs and wonder if you'd get our double buggy in the boot (easily fits flat in our 'normal' estate).