why do we add meg- before the verb?
I think it conveys some kind of perfect aspect (?)
I don't know much about aspects, but as a Hungarian native speaker, I'd translater the version without meg- as "The girls are kissing the boys."
Is meg- making it continuous or one-time? Are they kissing now or they kiss them usually?
It translates better to "The girls are kissing the boys," so continuous I think.