Here are resources related to preparing garden beds and cover cropping.
Video - Bed Prepping with Kids: covers checking for proper soil moisture, nod to adult bed prep, inefficiency by design, tips for digging with kids, amend with compost. At 6:43 video changes to furrow planting carrots with kids.
Soils and Bed Prepping with Kids from the Creating and Sustaining Your School Garden Training
--determining soil texture - Nitty Gritty lesson from Life Lab's Garden Classroom
Additional Resources - Going Deeper into Cultivation and Fertility
Soil Cultivation: Fundamental Concepts and Goals
https://casfs.ucsc.edu/documents/for-the-gardener/soil_cultivation.pdf
Your Soil - A Primer, with Some Strategies for Sustainable Management
https://casfs.ucsc.edu/documents/for-the-gardener/soil-primer.pdf
Choosing & Using Cover Crops in the Home Garden & Orchard
https://casfs.ucsc.edu/documents/for-the-gardener/choosing-cover-crops.pdf
If You Are Building New Beds or Buying Compost Here are Garden Bed Soil Calculators
https://www.gardeners.com/how-to/soil-calculator/7558.html
https://www.soilbuildingsystems.com/tools/cubicyardtoheight
https://www.soildirect.com/calculator/cubic-yard-calculator/
Life Lab's Garden Bed Design Guide (below) shares plans for the garden beds in the Garden Classroom Demo Garden Bed Site. This document isn't fully edited but it does share good information on building garden beds.