Answer: In my experience it works well to set a container of damp potting mix next to the mother plant, then place a spider plant offset or baby on the soil surface. Pin it down using a bent paper clip to keep it upright and in contact with the soil. Eventually it will root. Once it has rooted, sever the connecting stem. Or, you can separate them off and make a mini greenhouse for the babies as illustrated in the following web page, under figure number 5. (You may need to cut and paste the complete url into your browser to make it work correctly.)
Remember to keep the soil moist and provide as much humidity as possible while they are forming roots. I hope this helps!
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