Pa-pa is bye-bye. THe other similarly sounding "papa" are used for "food" especially by small children learning to speak (are easily pronounced by them) and means indeed food. Please note the difference: "pa-pa", (which can be also said just by it simple "pa" form, meaning "bye", not the repetitive"bye-bye") and the other "papa" (writen in one word) which is then colloquial "food" (used mainly for infants)
I actually come from the interesting situation where I grew up in a Romanian family (My mother's family sought refuge in the US amidst extreme religious persecution by the securitate, the romanian seceret police of the Ceaușescu regime, in 1986.) I was born in 1995, and was never taught Romanian growing up (hence why I am here now) but little things did bleed through. Papa was one of them. My sister and I would be told things like "eat your papa" (eat your food) So the difference between papa and pa-pa actually makes sense to me. When in doubt, I find that context plays a huge role in every language!