小 + animal is the standard pattern for Chinese pet names and childhood nicknames (
小虎 'little tiger',
小龙 'little dragon',
小鱼 'little fish').
小虎 in particular evokes courage and energy — parents pick it for active boys. The Taiwanese boy band
小虎队 (Little Tigers) made the name iconic in 80s/90s pop culture across the Chinese-speaking world.