The best method really depends on the types of weeds that you have, and the least toxic methods are non-chemical (ex. hand weeding, mowing, tarping, mulching, etc.). Low toxicity pesticides are those labelled with the signal word "Caution" rather than "Warning" or "Danger". You may consider some organic options, such as corn gluten meal, but that is a pre-emergent herbicide (i.e. needs to be applied before the weeds emerge). Horticultural vinegar, or acetic acid, is effective in killing some weeds, but beware vinegar herbicides with more than 5% vinegar can cause skin damage and eye damage. When using a pesticide, always read and follow all label directions. You can find more information about herbicide toxicty, including searching by active ingredient, on the National Pesticide Information Center webpage: https://npic.orst.edu/.