My son Eli has been using iPad apps since he was one and we have about 50 toddler apps. With the big caveat that this post is based off essentially a sample size of one, here are some toddler app user interface guidelines.
- Load the app as fast possible. By this I mean two separate things: first, reduce the time it takes to press the icon and be able to interact with something on the screen. If this takes too long, impatience sets in and the app is likely to face the gong (home button).
Second, reduce the number of screens before the actual app appears to zero, i.e. go right into the app. Yes, I understand you want to upsell and do other stuff there, but just don't. When you do that, especially when put links to the app store there, the toddler will click them, and then get confused. For example, Park Math is a great app, but I hate their home screen -- that big yellow bus is so attractive to click!
- Move all settings out of the app. For iOS at least, you can move settings out of the app and into the general settings window. Please do this because toddlers are drawn to your little setting icons, and they a) destroy the flow of the app and b) the toddler will change all of them and put the app into an annoying state, e.g. in another language, too hard for them, etc. Interactive Alphabet is another app we like, but it really needs to drop those 4 unnecessary buttons on the bottom of the home screen.
- No pop-ups/notifications. See a theme here? If there is a non-app associated thing the toddler will click it :). Pop-ups are the worst because they are modal giving them a 50/50 chance to click on the wrong thing. They're just not appropriate in these apps. There must be a presumption in these scenarios that the parent is controlling the app at that point, but at least in our household this is usually not the case. He scrolls through the screens and picks the apps he wants to use.
The worst offender I've seen with this point are the Dr. Seuss Apps. These apps need work in general and I don't really recommend them, but this aspect particularly annoys me.
- Make everything tappable/clickable. Toddlers love to interact with the app and point out and press everything. When things respond to those taps, it makes the experience a lot better. Itsy Bitsy Spider does this really well.
- Change it up/give surprises. The best apps not only make everything cilckable, but also do different stuff from screen to screen and even hide games/easter eggs. For example, a click may do something but a long-click may do something else. In a book, one page you may have to color and the next page you may have to click a series of things. Jack and the Beanstalk by Ayars (there are several) does this excellently. Here's an example page where they have this mouse dragging game action built in.
- Give multiple ways to do things. Sometimes it is unclear what to do, or the toddler hasn't mastered a way to do something, e.g. the swipe motion. So it is better to offer an alternative. In the swipe example, little arrows to turn pages work well.
- Give hints. If there is no activity for a bit, it is great to give the toddler a hint of what to do, e.g. by highlighting something they could/should tap. A similar behavior is to offer a mechanism to get hits when something is hard to do. Animal Hide & Seek Adventure does this well. You're supposed to tap the hiding animals, and they offer a dock on the bottom to shake the animals if you can't find them.
- Add delays. Once a toddler understands how to do something, like turn a page, they want to just keep doing it. But this leads to them doing things like rushing through the app without really getting much out of it. The way around this is to delay some of the interface elements (including hints). For example, instead of showing the arrow to the next page right away, wait 5 sec. for doing so. I actually haven't seen anyone doing this yet, but would really appreciate it. The same goes for hints, i.e. the animal game I mentioned above. It would be better if the hint dock did not show all the time.
- Give instructions. Literally tell the toddler what to do, i.e. speak instructions to them. This can be done in conjunction with the hints and delays mentioned above, and also at the beginning of a task. Monkey Preschool Lunchbox (also on Android) does this very well.
- Update the app. It's great when you can update the app and the toddler can see the changes. It doesn't have to be new features, but could just be new themes or other look changes. Elmo's Monster Maker does this well by releasing seasonal and holiday updates.
- Highlight words and letters as you say them. When reading to the toddler, I think it will help them associated words and letters with the sounds better if you highlight what you're saying as you're saying it. The Monster at the End of This Book does this well.
Finally, here are some gripes with iOS:
- Home button needs an off switch. I need some way to disable the home button or make it harder to access during app play, e.g. a triple click or some other morse code sequence.
- Need a way to hide videos. Eli knows how to get to the videos. He can find the icon no matter where I put it. I can disable videos through restrictions, but that doesn't really solve the problem. I would really like to be able to hide this icon like you can do for system icons on Windows. Another option would be to put the restriction on the icon itself and force me to enter the password when clicking on it. Come to think of it, this would work for the home button too.
Update: there are tons of excellent comments below, including many from great app makers and other parents like myself. Here are some additional guidelines.
--Setting to disable photo taking.
--No in-game purchases.
--Cheer for the toddler when they do something right.