Answer: It looks like you might have a handful of strikes against you in your first gardening experience. I hope this year's results won't keep you from trying again next year! To begin with, 8" is a little too shallow for most plants. And, while you lined the boxes with hardware cloth for good drainage, putting the boxes on a concrete slab will keep water from draining properly. Crows like seeds, and squirrels will dig most anything out of the ground, so they may factor into the failed garden experience as well. Since you didn't say whether or not the boxes are in full sunshine, nor did you say how often things were watered and fertilized, I'll have to count those things as possible problems, too!
Raised beds filled with 3 in 1 soil are excellent ways to raise vegetables and grow flowers. But, most plant roots will need a depth of 12"-18" of soil to give the roots enough room to develop and support the plants. (Some exceptions might be small annuals.) Perhaps your Father-in-law can be persuaded to add another 8" board to the boxes to give your plants 16" of soil depth. I'd suggest either moving the boxes to a better draining area, or putting them up on 2"x4" blocks to allow water to drain beneath them. If the boxes are in full sunshine, the concrete will reflect heat onto the plants and into the soil. With such a shallow depth of 8", the roots probably cook every afternoon! Finally, if crows are a problem, you may want to lay birdnetting over the newly planted boxes to protect the seeds. Once the plants are 4"-6" high you can remove the netting because the plants will be big enough to take care of themselves. When your veggie plants are up and growing be sure to provide water as often as necessary, when the soil begins to dry out.
Following the above suggestions should result in a thriving, productive garden. Better luck next season!
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