Dragonfly larva are voracious.
So long as you are sure it is not a hybrid, in which case it will not have offspring like the parent.
Lawns don't need water. If they go very dry they will recover when we have autumn rains. Most native trees don't need water either.
Put water butts on your downpipes. You will be amazed at the amount you will collect. Then get yourself a cheap pump and you can move water all over the place. I wouldn't sacrifice most of your patio.
You don't say how old the child/children is/are.
Do you mean they should have been planted in Spring 2013?
Sorry to suggest this, but I would buy some plants in case yours never take off.
Glyphosate becomes inactive once it hits the ground. Just so long as you have 6 dry hours after you spray the glyphosate will do the job.
But do put the rotavator away or you will make the weed problem so much worse.
One of the most valuable plants is the humble nettle as it is a food plant for several kinds of caterpillar. Flowers are fine for nectar, but if the caterpillars have nothing to eat they're done for!