I just have to give a shout-out to what I think is the coolest toy innovation for kids: foam puzzles. In all fairness, we actually only have one foam puzzle, but it's fantastic!
After our kids graduated from the shape puzzles, where you drop characters into their corresponding shapes, we tried to buy them miniature jigsaw puzzles (the classic cardboard kind). We also purchased wooden puzzles. Neither of the kids liked these. They would try to shove pieces together, and Jo especially would get angry when the puzzle pieces didn't lay flat or got slightly bent.
I was browsing Zulily for Easter gifts this past winter, and they had a Frozen foam puzzle (25-pieces) for almost nothing. Not knowing what to get Jo (and knowing she likes Frozen), I decided to get it for her. It's been a big hit with both kids. Oliver was able to piece it together himself right away, but Jo needed some help. She liked to work on it with me, and we did so regularly. Fast forward a couple months, and she's putting together by herself completely. She puts it together, pulls it apart, and puts it together again.
It's also hard to break. She can pick it up, move it around, and the puzzle isn't falling apart. It saves on tantrums. There are few products I feel are just so great, but this is one of them. I then went online to find a foam puzzle with more pieces. We're now expecting a 98-piece Cinderella puzzle in the mail, ha! But at least it'll be a good challenge for quite a while.