1. First decide what you want to grow, and purchase your seeds. Instead of a big garden this year, we decided to start seeds for cooking herbs that will go in a small kitchen garden. Also, some lavender. Not all seeds need a head-start indoors, so you’ll want to do a little homework. The information you need can usually be found on the back of the seed packets.
  2. Gather your supplies. Wash and dry your yogurt cups. Carefully, use a drill or knife to make a small drainage hole in the bottom of each container. Make your own seed-starting medium or purchase seedling soil from the garden center. I opted for convenience this time and picked up a bag of seedling soil from the garden center. It was reasonably priced and saved me the dirty job of mixing it up myself. You’ll also need a garden trowel. Since my 9-year old would be using it, I picked a small plastic one that worked great.
  3. Moisten the seedling soil some before placing it into the pots. Have your children fill all the seedling containers with soil. Kids have so much fun with this step!
  4. Kids can also place the seeds into the little pots. Some seeds are very small, so younger children may need some assistance. Poke a small hole into each pot, sprinkle in a few seeds and gently fill the hole with soil. Some seeds require deeper planting, so be sure to read the back of the seed packet for directions. If have a variety of seeds, it may be a good idea to label them. Popsicle sticks and a marker work great!
  5. Water seeds after planting. Be careful. A stream of water can dislodge seeds. In my experience, children have a tendency to over-water, so we mist using a large spray bottle now.
  6. Your seeds need water to germinate, so check daily to make sure the mix stays moist, but not soggy.
  7. Most seeds germinate best in warm conditions, so move your seeds to a warm spot. Also, if your air is very dry, you may need to cover with plastic wrap.
  8. Germination time varies, so I recommend keeping a seed planting journal so you’ll know when to expect your seeds to sprout. It’s a wondrous moment when that first seedling emerges!
  9. Good light is essential to plant growth. When you see the first signs of germination, move the plants to a light-filled area.
  10. Once seedlings have grown enough and have true leaves, you can transfer them to a larger pot.

Reference: https://www.aboutamom.com/upcycled-seed-starting-project-for-kids/