But then there's little use until 1980s. See the Google NGram app that searches for usage in books: https://books.google.com/ngrams/graph?content=nerd&year_start=1800&year_end=2000&corpus=15&smoothing=3&share=&direct_url=t1%3B%2Cnerd%3B%2Cc0
I think there are two things to remember. I worried about Ethan too. Because it's 2018 and we're paranoid about our children now. But it's 1958. Friends and strangers 'looked out' for your wee one quite often. That lady did say she'd watch him for Midge just before she joined the rally. It was a completely different time in the 50s where people loved their kids; they just weren't paranoid. The second thing is that this show is not a gritty realism type show where you expect true life. This is a beautiful musical type genre where reality is displaced for awhile while we enjoy the swelling music and aesthetic placement of people and things. Don't get confused and expect it to be everything all at once.