From the NY Times,
"Their father has the only key to the front door, and he keeps it locked. In some years, they are allowed outside only a handful of times. In others, not at all."
The sentence is too ambiguous for me to understand. What I understand is that, their father had only one key for front door. After some years they are allowed to go outside. After that, it's as in the last sentence: "In others, not at all." I don't get that part.
Is that grammatically correct, if yes what does it mean?