Generally speaking,
1. If this has been gone into in great detail previously, then use "was." If not, use "were."
2. If the situation is threatening to the kids, use "was." If not use "were."
3. "Were" has to be used here. The initial "was" in the sentence decides this: two "was's" in a row would be awkward.
4. "Was" has to be used here. "Was" matches