check out the outdoor mega store online, they've got some good stuff cheap.
you might want a cooker stand - especially with the kids around. a table next to the cooker stand for prep as well. the picnic table previously mentioned is great.
lanterns for a decent bit of light at night - we all crowd into our bed and read a few chapters from our kids story book before they drop off!
wind breaks! last trip to NOrth Devon was soo windy!
some sort of water carrier/store, a chilli bin, cheap plastic picnic set, kettle, pan set, utensils, storage bin for all of the above.
i find it easier to have a full camping set rather than raid the kitchen coz i always forget something or it doesn't make it home!
we do the blow up double bed for us and singles for my skids, dd was still in travel cot this year so...... the skids have sleeping bags but we take duvet/pillows. electric pump with car adapter!
washing line, washing up kit etc.
an extra groundsheet is always useful for outside so you're not traipsing dirt in every time.
hth, can't think of anything else off the top of my head!
welcome to the wonderful world of camping - i love it!