For a medicinal planter, you will need a big container, preferably about two feet across. A barrel is good. You can get a big wooden box and line it with trash bags, or use several smaller pots grouped together.
Especially good for children are the scented geraniums for potpourris and sachets, and mint and chamomile they can make into tea. The geraniums are very easy to propagate. Just break off a branch and stick it into a pot of soil. Mint is a weed. If you don’t keep it in a pot, it can take over the whole garden. Mint comes in a wide variety of scents and flavors and is very easy to grow.
If you have the right climate and can grow hibiscus, the red flower makes an amazing tea. Not only is it delicious and healthy, but when you put the flower into a cup and pour boiling water over it, the flower turns grey and the water turns jewel-like red. Talk about magick!
There are many others. Goddess is generous with Her herbs.
Comfrey and plantain have large leaves that form a wide rosette close to the ground. You need a wide planting place for them. Comfrey can grow to two feet in circumference. Both can tolerate some shade and neglect. They are not good pot plants.