"When I look back, I am one year old again; the children clap their hands, happy to meet the New Year again." It is a couplet, which means:
As soon as the old man turned around, he suddenly became one year old again. Unconsciously, I have grown one year older; the child clapped his hands happily because it was the New Year again.
Note: In addition to specifically referring to the founder of the Taoist school, the word Laozi was often used to refer to older men in ancient times.