Baby Hummingbird in the Cold?

I found a baby hummingbird-- it has some green iridescent feathers, but still some of that fluffy white stuff-- sprawled flightless on the concrete and could not locate its nest. After determining that it was not injured, I placed it in an old shoebox with cloth and toilet paper and fed it sugar water until his mom found him after she heard him crying. All day, she has been feeding him on our balcony every 20-30 minutes (we’ve been clocking) and now that it is dark, she’s not returning (probably sleeping). The baby has also gone to sleep now that it is dark, but it is going to be a rather cold night… 50 degrees Fahrenheit (10ish Celsius). Should I bring the box inside for the night, providing I keep the baby in the dark so that it doesn’t think it’s day? (My parents are pushing me to “save the baby from the cold,” but I’m not sure if a night in a warm, cozy house will spoil it.) Please reply quickly, what do I do?