Ah! The age old dilemma of a good lawn and pets! I should mention that a study at Purdue University found that homeowners who use weed and feed type lawn chemicals increased their dog's risk of developing bladder cancer. You really have to choose carefully what goes onto your lawn.
I've heard of Weed & Feed(it's made by Scotts). It's not supposed to be harmful to kids/dogs if used properly. "Properly" sounds time consuming, and I wonder how safe it is if a dog was to eat some grass, and not just walk on it. Maybe you want to email the Scotts company, and see what they recommend.
Scott's Weed and Feed's directions say: Apply on a calm day to dry soil and then water in well using plenty of water. Allow at least 1/2 inch of water to dissolve the pellets. This can take 2-3 hours using a garden hose sprinkler or a day long rain in most cases. Once the product is washed down into the root zone it is safe to let kids back on the lawn.
Look for lawn care products that are natural and non-toxic, such as the new line of Pet Approved lawn and garden products from St. Gabriel Laboratories:
St. Gabriel Laboratories' BurnOut IIhttp://www.biconet.com/lawn/burnout.html
Some other products which are safe for dogs, and yet kill weeds:
White vinegar makes a great weed killer. It has to be used properly to do the job but that's true of almost anything. And it is very safe - endorsed by organic gardeners & used by railway companies to kill vegetation along rail lines that would cover tracks.
Ordinary strength vinegar(5-6% acetic acid) is used. To a gallon of vinegar, one would add a 1/2 tsp of dish detergent to act as a surfactant so the vinegar would penetrate the soil well & move down the root. Put the vinegar into a large squeeze bottle(for a small job). For larger jobs, use a garden sprayer that will deliver a thin stream instead of a wide spray.
You need to trim off leaves of weeds that cover the root(like dandelions, plantain, & other low growing weeds) but if the leaves aren't in the way, don't worry. Just make sure you aim the vinegar stream down to the ground & just around the root. It will penetrate & the weed will die in a day or two. If you spray it around, the grass or other plants will die too. It's best not to use in a mixed bed where you don't want to harm other plants. The vinegar kills the weeds by disrupting the normal pH around the root but is quickly washed out after a rain or if one waters the lawn well. After a rain or two, you can re-seed the bare patches with no harm. One more important thing - do this on a SUNNY HOT day for best effects. If you try it during cool or wet weather, your results will be poor. It needs a few days of hot weather to do the best job.
An old time way to kill a few yard weeds easily and without chemicals is a kettle full of boiling water. A half cup of boiling water on a dandelion soaks down and usually kills root and all. Use a Thermos to keep the water boiling hot as you carry it outside.
Wow!(and Wow! Plus)- are a byproduct of corn syrup production, and controls germination of broadleaf weeds like dandelions and crabgrass, but it's not poisonous so you can let your dogs out right after it's been applied. WOW Plus is the original stuff plus a balanced all-natural fertilizer.http://www.gardensalive.com/product.asp?pn=2289
RoundUp- has an active component breaks down into harmless compounds- doesn't persist in the soil. It's an herbicide- won't affect insects or animals. http://www.roundup.com/
I've read that the secret to a good weed free lawn is to have a healthy lawn, and you will not have weeds. Fertilize with a good fertilizer 3 times a year, add a organic fertilizer with plenty of nitrogen and potassium, but very little phosphorous(the middle number on the bag). I've been told that phosphorous encourages germination of weed seeds and is already present in adequate quantities in most lawns. Remember that the Fall fertilization is the most important one.
Unfortunately, the same products that produce healthy lawns can sometimes cause health problems for pets. North Country Organics in Bradford, Vermont is one company that offers a good lawn fertilizer: Nature's Turf, which is an 8-1-9 fertilizer. Blue Seal Feeds has an organic fertilizer, Safe and Simple Lawn Food, that is a 6-2-4 that is made from soybean, alfalfa and fish meals. You can use the same organic fertilizers that are available for vegetables and flowers, on your lawn. Although organic fertilizers cost more, they generally use ingredients that are released more slowly over time. This means they won't all wash away with the first heavy rain.
I hope that helps!
Best of luck,