re: Daughter (8) opened her big gift from FedEx today, super bummed.

Wrap it up as a gift from you instead of Santa. That way you get credit, not Santa.

or, just get some games for Christmas morning.

Later in the week wrap up something horrible in a box and leave it on the doorstep, when she opens something else that isn't hers she'll regret it.

Teach the kids that it's illegal to open other people's mail.