Companies that have earned their reputations developing great toys for toddlers and preschoolers are entering the infant realm with new lines for wee ones. Kid-O will introduce a baby gym and several rattles in June. PlaySkool will introduce the GlowWorld line of newborn toys, based on the popular Glow Worm, this Spring. Plan Toys will debut the PlanBaby line, including the Rattle Mobile, later this year. And Sprig Toys' Baby Sprig line, including a stacking toy and rattles will hit stores in June.