Safe (for kids) way to kill Oxalis/broad leaf weeds

You don't need a lawn that looks like fake grass. Having some "weeds" can make it more beautiful and welcoming to wildlife. If you let the dandelions grow, butterflies will come to nectar. A diverse habitat instead of a sterile lawn will invite insects which will bring birds to eat them. Think of it as a meadow instead of a lawn. If you try to keep it just the same as when it was put in, you will make yourself miserable. Enjoy the evolution and the sturdy plants that add themselves to the area. I definitely prefer weeds over toxins. 

Oxalis is really invasive. I think if you try poison you will kill your grass too. You need to pull it out by the roots, including the tiny bulbs.  You have to keep at it, but eventually you will get them all out.  I actually find it pretty satisfying to pull oxalis, if the ground is moist like now, after the rain. Get yourself a Japanese hori-hori knife. Or use a sturdy knife that has a 4" blade at least. Stick it straight down into the soil about an inch away from the base of the oxalis and then grab the oxalis cluster just at the base and gently pull it out.  It's fun! I once paid my kid and his friend a quarter per oxalis (with roots intact only!) and got my whole yard cleared of them in an afternoon.

Gardener Mom

Sorry I missed your post the first time.  Wow was I in the same boat last year.  It was my first year with a new garden and it felt like an invasion.  So this is what I've learned so far.  I initially thought it was important to pull them up by the bulb and that would "get rid of them".  I was surprised to learn that for that one bulb there are several more below the ground energized to send another oxalis sprout up to the surface.  From searching the internet and extensively questioning multiple gardeners my best advice is this.  If it is a garden that has not been weeded in a long time you may have A LOT beneath the surface.  Cardboard sheet mulching will help somewhat but will not entirely solve the problem.  Cardboard sheet mulching combined with diligent weeding every week or two during this oxalis rainly season will exhaust the bulb and in a couple of years, yes years, you will see dramatically less oxalis.  There is no chemical pesticide that will work for this.  If you were going to start a garden you could lay black vinyl over the space but it would take months before you could start your garden and you would have to provide nutrients to the soil.  All in all there is no easy solution.  Don't despair that more will pop up RIGHT AFTER you weed.  Just know that it is a process that will take years.  I'm in that process now and have just decided to throw money at the problem by hiring weeders.  If you want to see a good website regarding oxalis you can look here http://wric.ucdavis.edu/information/natural%20areas/wr_O/Oxalis.pdf.  Best of luck.  Thank you for taking this challenge on.  You will notice a lot of homeowners in Berkeley have just given up the battle.  And also, Oxalis will hurt other plants and really does not fit into the pretty wild meadow look as far as I can tell.

We have an oxalis infestation in our front yard, and I'm a librarian, so I've done extensive research on it.

No chemical works on oxalis according to the experts. So don't bother. As a previous poster suggested: the only recommendation I have found is to pull the oxalis by the roots or dig it up and be careful to catch those white "bulblets" - if you leave those, you'll get more oxalis. And be persistent, get them young, and hopefully you'll eventually wear out the plant enough to stop. But keep in mind: this is considered one of the top three most pernicious weeds in the world, so it's not going to be easy or quick. I am hoping the persistent weeding and digging eventually does work.