At the top of the list are Wood Puzzle HD (US$0.99) and My first puzzles HD (US$1.99). What stands out about these two in particular is the number (and variety) of puzzles that they both offer. Wood Puzzle HD comes with 15 puzzles, which include animals, people, shapes, and other objects. In contrast, the puzzles in My first puzzles HD are all of animals or wildlife.
With few exceptions, the user (err, toddler) interaction of both apps is similar; there's only so much that you can do when a puzzle piece fits into an empty space. One neat thing about Wood Puzzle HD, however, is that shaking your iPad scrambles the puzzle. And on My first puzzles HD, when a puzzle piece is placed in the correct spot, the piece is magnified and accompanied by applause.
Kids Puzzle provides feedback similar to that of My first puzzles HD. While it's difficult to complain about paying $0.99 for a wooden puzzle app, and for a baby no less, the value that Wood Puzzle HD and My first puzzles HD provide make them both stand ahead of Kids Puzzle (as well as other apps in the genre). Kids Puzzle comes with only one puzzle, which pales in comparison to Wood Puzzle HD and My first puzzles HD.
Ordinarily, I wouldn't include an iPhone app in a roundup of this sort. This would be like putting bacon strips in a peanut butter sandwich. But hey, a peanut butter and bacon sandwich is good in certain situations.
Likewise, despite being formatted for the iPhone's screen, the Thomas Game Pack (US$2.99) works well on the iPad's screen in 2X mode. As implied in its name, the app features every baby's favorite train, Thomas the Train, as well as his favorite friends. Each of the wooden puzzles are in the shape of Thomas and his friends (Emily, James, Percy, etc.). In addition to wooden puzzles, there's a matching game and a cargo maze. If your baby is a Thomas fan, he'll love this app.
While the tangible feel and interaction with physical puzzle pieces bring immeasurable qualities, they come at a price. Let's face it, wooden knob-based puzzles can become quite costly, and there's a chance that a piece or two might go missing. Given their fairly reasonable prices, iOS-based alternatives are a good complement to their physical counterparts.