Check YouTube for a number of suggestions. If you are on the move and don't have time to do a home reveal, some of the videos will help. Our grandkids love scavenger hunts of all kinds...scatter letters around the house (or hotel room) that, when put together, expose the surprise. Good luck!!
You can also see plenty of surprises gone wrong - where the kids were NOT happy about it. For many people - even kids - anticipation is half the fun and getting something like that sprung on them is not a joyous event.