There's no established meaning for "preschool kiss" or a separate meaning of "kindergarten" beyond its standard definition. "Preschool kiss" sounds like a made-up term, possibly referring to a light, playful kiss between young children in preschool, or perhaps a metaphor for a fleeting, insignificant event.
Kindergarten refers to a year of preschool education for young children, typically aged 4 or 5, before they enter primary school.