I like to garden. Its in my blood so to speak (I have 5 generations of non-farmers that I know of that were avid gardeners).
I like raised gardens to make it easier on me and my kids. When I do raised gardens I put bricks or blocks or landscape timbers around the area I want to garden in and fill the area with compost, manure, top soil or potting soil. I use rabbit, steer (cow) or chicken manure. I don't use horse manure unless I know what the horse ate.
Why so picky about horse manure? Because the horse's digestive system is not very thorough. Weed seeds don't decompose or digest completely. So if the horse ate run of the mill hay, you get the weed seeds that are part of the hay in your garden. I found a lady that did competitive barrel racing. She bedded her horses down on cedar and pine shavings and only fed her horse oats and a special hay. It made a wonderful garden soil.
A real good book for maximizing your back yard garden is "Square foot gardening". You can go to youtube and find some real good videos on raised gardens. A good video I've been watching lately is: http://www.youtube.com/watch?v=AKrkaSf8aT4
One of the things I'd recommend for kid gardens is to have the kids plant what is interesting to them and something they like to eat. Then when it makes it to the table, you can praise their efforts and how good their produce tastes.
I make my raised beds 4 feet wide and how ever long you want. Why 4 feet wide? Because weeds are so much easier to pull out of a raised garden and my reach is just over 2 feet. I can lean over and stretch and get more, but 2 feet is easy. That way you can reach both sides of a 4 foot wide raised garden.
Good luck to you and yours.