The I Spy will work, but won't keep their attention for long. I still plan on giving them some of those extreme dot to dots, mentioned here. But I have been racking my brain on any other ideas.
That is, until I came across this post by fabulous A Subtle Revelry. For a bridal shower, they made photo puzzles. They printed out a bunch of different pictures for the engagement shoot, cut them into squares, and then put them in burlap bags for people to take.
I think I will also spray mount the pictures to different colored purple cardstock, to give it a heavier texture, and so if they mess up the pieces they just have to look at the back color.
Not sure what I will put each one in yet, but excited for this DIY!