Thank you for reaching out to Ask Extension.  To prevent aphids you should cover the plants as  you plant them. Check that the transplants do not have an infestation already.  Aphids are most active in May and June.  Remove the cover when the plants flower to encourage pollinators.  You will need to continue monitoring throughout the growing season.  See this factsheet for more information on aphids on vegetables.

https://extension.umd.edu/resource/aphids-vegetables/

The best way to protect your plants from cabbage worms is also a cover.  You need to prevent the moth from laying eggs on the plants.  See this factsheet for more information on cabbage worms.

https://extension.umd.edu/resource/imported-cabbageworm-vegetables/