If the soil is soft enough I would dig it out eighteen inches and then mesh dropping the sides down also then re-fill with soil. saves on flooring and gives the chips something more natural to dig in and plant their own garden.
Mine have grown sunflowers all manner of wheat barly and corn along with various grasses and a wierd looking thing which may belong to one of my elder boys

they thouroughly enjoy planting and weeding and especially now it is time for the harvest they love picking out the seeds from the grasses and corn.
You may also wish to think about installing a sturdy comfortable seat so you can enjoy time with them without getting a bad back

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I also recommend large white flexi hose as used on tumble dryers..... tell the wife it was stolen while you were away

happy building whatever your decision, look forwad to seeing the finished article with chips..