1
general::
Also, calf love. Adolescent love or infatuation, especially one that is not expected to last, as in Beth is besotted with him, but we think it's just puppy love, or He's got a bad case of calf love. [First half of 1800s]
American Heritage Idioms
2
general::
Phrase(s): puppy love
Fig. mild infatuation; infatuation as in a crush. (Used especially of adolescent relationships.) • Is it really love or just puppy love? • Look at them together. It may be puppy love, but it looks wonderful.
McGrawhill's American Idioms And Phrasal Verbs