If it gets sufficient sunlight then I think this would be perfect for a child's veg patch
Plenty of room to grow lots of stuff in there
And the path up the middle would serve as a good divider from which to weed, plant and water etc.
I think the conifers may have depleted the goodness in the soil quite a bit so the first thing you will have to do is double dig the area.
Basically this means digging down a spade's length all over and putting the soil on either side of the bed on a heap. Then dig down a spade length's more picking out stones and roots as you go. By this time you should have a thoroughly dug patch plus two big heaps of soil on either side of it (it's hard work).
Then go and buy or beg as much compost or soil-enriching material such as horse manure as you possibly can (sterilised is best from garden centre if you are planting veg as you don't want lots of weeds in it).
Mix the compost material in with the heaps of soil and replace in bed.
Leave a few weeks to settle and then rake over the earth again so that it is has a fine texture ready for planting.
Then plant loads of child friendly veg such as runner beans up poles, sunflowers, marigolds, chives, radishes, lettuces etc etc
Weed and water regularly and you are away!
All of the above is dependent on how much sun that patch gets however.
If it's not much then some shade loving plants would be better ...
Your dc are gorgeous btw!!!