Could it be creeping Charlie?

It is violet, Viola species. These seed very freely and are often difficult to eliminate from lawns or planting areas. Try a herbicide with triclopyr as the active ingredient.

I've had excellent results with controlling violets in KBG turfgrass with a product called Crossbow mixed 2oz to the gallon w/surfactant like Dawn dishwashing liquid in a gallon sprayer and spot treating.

Like many other herbicides, do not apply in high summer (80° to 90° F +) temperatures or, when the turf is stressed or under drought conditions it will tend to damage the turf wherever there is any overspray. Spot treatment works great, but you'll have to hit them more than once. As in, whenever you see them re-emerge. Keep the fall fertilization regimen going and normal cultural practices that encourage a thick, healthy lawn and that will help to keep them from finding a foothold. Here's the label instructions, it's a mixture of 2,4,D and Triclopyr. It's of course good for many other broadleaf weeds and woody plants as well.

http://www.cdms.net/ldat/ld02h006.pdf

Where do you live?

What kind of grass do you have? Triclopyr will kill some grasses.

Sorry Im in no way a gardner. If you cant tell by the picture I have no idea what the name of the grass is. Im in Ontario Canada if that helps. I know in the States you guys have more options. The restrictions in Ontario are unreal. I have to by my 24/D4 and concentrated roundup in the states when i go.

Im going to try EcoSense Weed B Gon to kill the above weeds as soon as I get a day without rain