Weed killers vary in toxicity but the most important factor is how much you use and how long you allow after spraying before letting pets and people onto the lawn.
That said, the safest herbicide is corn gluten meal, but it acts to prevent weed seeds from germinating, not to kill existing weeds. The clover and other cool season weeds you see now will be dying soon. I suggest either hand pulling or mowing and ignoring them. Focus on proper mowing, watering and fertilizing to build a dense lawn which will choke out the weed problems over time.
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