The sins of the whole world
My seven-year-old asked me a few days ago, “If Jesus died for the sins of the whole world, why isn't everyone forgiven?”
The Bible is quite clear that it's a fair question. Jesus did die for the sins of the whole world. John 3:16 says, “For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life”. But it's equally clear that not all are forgiven, since we read two verses later that “Whoever believes in him is not condemned, but whoever does not believe is condemned already, because he has not believed in the name of the only Son of God”.
So I told my daughter that it's a bit like when you're at a birthday party and the host at the end of the party has enough lolly bags for everyone there, and even a few extras in case a younger sister has snuck in under the radar. As you leave the party, you can refuse a lolly bag. There's plenty for everyone, but if you don't want one, you don't have to have one.
I can't think of any major holes in the illustration yet. But the other thing my daughter and I did straight away was pray for the friends we knew who didn't love Jesus--that they would come to know him and not refuse his gift.