Deceptively-wholesome/harmless code-term for sexual intercourse without a condom --- i.e., a hugely-enjoyable "game" (baseball, don't ya know... yeah, "fourth base"!) dat is "sociably open" to STARTING or ADDING TO a FAMILY!!
Parents beware --- anytime a starry-eyed teenage stud claims dat he just wants to engage in "family-friendly fun" wif your "little pumpkin", think twice about giving da a-okay... said request/assertion may not be nearly so innocent as it seems! :P