Boric acid is toxic as is ALL flea and tick stuff, or else it wouldn't kill the fleas, right?
The key is to sprinkle it liberally on the carpeted areas of your home then rub it in HARD so you don't see that it is there anymore. It is a natural item (I mean it occurs in nature) so it is not a chemical with unknown consequences. Wait a week before you vacumn again. I also sprinkle it between the box spring and matress on our beds and underneath the cushions on the couch. Again, I rub it in hard. You don't want to eat it, and you don't want your pets to eat it, but applying it in this manner is safe and effective against fleas. Other flea ideas, cedar in the pets bedding (it doesn't kill the fleas but will repel them-they don't like the oil) or citrus based oils and sprays, again it doesn't kill them but will repel.
I have a three year old daughter and have had cats all my life and a yellow lab for the last two years. We do not use anything else, such as Advantage or Frontline, and we never have fleas.
I wish you luck!
Sarah