Seedlings and young plant like warm media to grow in. They like 22c+ . I've found 28c to be a happy place for them. Lower than 20c and you'll notice growth slow. <18c and it will crawl along. So 22-28c is best. Also, make sure your water is 22c-24c or you'll be cooling the roots and slowing growth when you water them. I got a heat mat recently for my Space Cookies (grow log on here) and it made such a difference I'm completely convinced they're necessary.
If they're buy an open window, perhaps put a dome over them to keep them ~28c with humidity ~60%.
But root temperature should not be overlooked.
