I certainly remember the difficulty of wielding an adult’s spade in our clay soil and am reasonably sure I’d have moaned less and enjoyed it more if my parents had put a bit more thought into what would make it better. It might even have kept me interested in gardening through my teenage years, which would have meant one more pair of hands in the garden.
So if you feel a bit like a Catcher in the Rye, trying to grab your kids before they disappear off the edge of the garden, Edmonton's Community Garden Network has useful design pointers aimed at community gardens on how to make vegetable plots attractive to children. The suggestions are just as relevant for home. They include making the beds small enough for short arms to reach across and storing water close by.
At the Gardeners' Club they list plenty of ways to make things easy and keep children interested, including making a spray bottle instead of letting them cope with a heavy watering can. And if you tend to exacting standards, there's a Parents' Primer at Kids Gardening, with a chapter on What Turns Kids On and Off Gardening. It might help you to relax. And reward you with children who stay to help.