Chalc - I have the same problem some years, there's just lots of things that find bean seedlings delicious. Try puting out a deep saucer of beer and see if you get any slugs. If not, if you have any old nylon stockings, cut off the ends at about the shin and slip those over the seedlings for a few days (tie loosely around the bottom and check daily to make sure they're not restricting growth) and see if that keeps the pests off. If no nylons, try just covering them with a light towel or sheet at night (if that's when the damage is occuring).
Depending on what kind of bug it is and if you can see it during the day, you can also try something called insecticidal soap. It's a soap so it's not poison, gets washed away by water and can be used on edibles. But it's a really acidic (or is it alkaline?) soap and so it burns through any bug skin that's not encased in a hard shell and kills'em...if you can spray it on them. My damage seems to occur only at night, which makes the soap difficult to use.
Also, there's a slug bait made out of iron oxide or something you an buy. It's not dangerous to kids/humans/veggies so long as you don't dump a whole box on anything...but slugs can't process it and they crawl away and die. It goes by various names including Escar-Go.
Anyway, garden looks awesome. Planted some bizarre asian melon seeds yesterday, we'll see if they grow. And waiting for the beans to come up. It's been a week so will hopefully be soon!
And OMG...the roses. Literally hundreds of blooms. I'm already planning a rose party for when they come out, it should be quite a sight! Also, I have Iris the size of a baby's head. It's one freaky year - and I'm loving every second.