Er, the idea is to also keep your soil growing from year to year. In other words, if you dismantle your beds at the end of the season what are you going to do with the soil? It would really be better if you could leave the beds intact over the winter.

What size of beds are you considering?

Do you presently have depth to your soil? (not rock right below the surface)

Ed

Tour local lumber yard will have material readily available for much less than that web site does. If screwing the corners together is not something you wish to do then you will need to cut the ends, drill through, and insert dowels (the pins) which is a lot more work.

no matter what you do, It will be great to do a garden with your kids.
You can screw 2 X 6 board to 4X4 post then drive the post in the ground, facing another set of post, then screw boards to the sides with no boards.
1 high, 2 high, 4 high. Most store will cut 2 X ^ X 8 's in half to make the ends of a 8' X 4' X X 12" deep bed.
I would leave it up year around & plant winter crops too.
It is not failure, to make a small amount of crops. It teaches children to work for a better out come.
If you make more the first year all the better.
No way to lose with a garden.

You didn't mention age of your children. That might influence the "crops" you plant ... [quicker results for younger children]

Whatever their age, hope you will keep a garden journal [some go online for this, mine is a cheapo notebook]Even long-time gardeners learn something new each season.

If you REALLY need to dismantle the beds at the end of the season - what about using straw bales as the sides? They are not expensive - you can easily build the beds with straw, and send them to your community compost at the end of the year - or get a local organic gardener to come and take them away and add them to their compost pile. Or, start a compost pile of your own! Straw works well, keeps moisture, and attracts worms.

Straw is not always that easy to come by, but feed stores have hay. Why not plant directly into it, then do sides when it breaks down? Quick way to get start with little work or prep.