When using lawn care products around children and pets a little caution is good.

If I was going to us a Granular Weed & Feed like Earl May Superfine which would be a good product to kill weeds and nourish the grass, I would only apply the product to say the front yard and keep the children & pets in the back.  After the granules have been on the lawn for two days (48 hours for best weed killing results), water it in and once dry, the lawn is safe for children and pets.  Then do the same for the back yard, fertilize back yard and children & pets use front yard, wait two days, water third day and children & pets out after it’s dry.

You could also use a liquid product like Liquid Weed & Feed , these liquid products are safe for children and pets once the product is dry.

If I just wanted to spray the lawn for some hard to kill weeds with Earl May Total Weed Control, the area is safe once the product is dry.