Short Story: I encourage everyone to make their own medicine. If you can grow it as well, even better. If you are in a legal state/country take advantage of your rights and help repopulate the earth with free medicine.
Long Story: It may seem complex. The information, especially in developed countries where the indoor marijuana market is front and center, is overwhelming. Hydroponics, nutrients, lights, fans, dehumidifiers, water quality, bugs, pests, oh my.
Forget all of that. If you are making medicine for your child, spring is the perfect time to start. Plant seeds or clones outside, in real soil, with real sun, and care for them as you would any other vegetable in your garden. Please do not use pesticides, especially Miracle-Gro or similar. If you have a sick child you should not be using those for ANY of your food (store bought included) but especially a medicine that will most likely be concentrated in the end.
If you like to tend garden, you can care for your cannabis plant in the same manner you would a tomato plant, including the pinching the suckers. But if you know nothing about gardening and prefer to buy your product, look for outdoor, local, organic flower. Of ask if your product was made from a plant grown in this manner.
There are many online resources for growing cannabis. Some years it will be great, others not so much. Even if you just throw it in the ground or in a pot with soil and never look at it again, it is a start. You may get an ounce/30g or you may get 2 pounds/1k, but you are growing something in your own backyard for your own use. I have a friend who did nothing but forget all about her plant in a drought for an entire summer. It survived and although it did not produce much it, with 4 plants it was enough to make medicine to last 6 months.
If you live in a developing country or area where weed grows wild, great! This is the best you can use. If you are unsure of the conditions or pesticides used in the production of your flower or product, drawbacks may outweigh the benefits. You will have to be proactive in your search. Or again, grow your own or find a friend who has a green thumb.
This is a great website for reference. https://www.dutch-passion.com/en/news-and-development/the-first-time-grower/