Precocious, not precious. In the chapter of Yotsubato this is parodying, Yotsuba (Nanako) goes to ask Fuuka's (Chie's) mom what heartbreak is, and Fuuka's mom says "My aren't you precocious." So not fully understanding, when she tries to cheer Fuuka up, she calls her precocious.
Don't feel down!UmmAhNanako-to!Chie is a precocious child!Precocious child!Precocious child!...It is a little painful...Isn't that painful?Are you all right!?Chie!Are you ok?!What are you saying?!UmmSo cheer up!My heart!But what really hurts is...What was itYukiko has never been heartbroken!