I know, I know, it's all good! I'll have sweet dreams of you Jo! lol
Don't worry about the blanket thing. If it caught on fire, I think you would know and would be able to stop it. They just say that so you don't leave it on while you're out of bed so your whole house doesn't catch on fire.
Let the kids use their imaginations. They can probably come up with games and stuff to do on their own and you'll just have to watch to make sure they don't get hurt. You can play hide and seek, tag, capture the flag, etc. The games can be modified to play inside. As for snacks, ask the parents what they prefer and if they have any info they need to give you about their children.
