Q: A few months ago you talked about limiting screen time for toddlers and the importance of picking good quality games for when we do allow screen time. There seem to be in infinite number of choices out there. How on earth do we know what to pick?

A: There are literally hundreds of thousands of educational smartphone- or tablet-based apps aimed at kids. Product sellers in the various app stores will assure you that their app will make you rich and your child smarter, taller, and more beautiful. However, just because an app is being sold by a big-name company, like Apple, Google, or Amazon, is hardly a guarantee that it’s (a) educational, (b) high quality, and/or (c) appropriate for your child. Here are some guidelines to keep in mind, some of which were suggested by Stamatios Papadakis and Michail Kalogiannakis, from the University of Crete; Heather Kirkorian, from the University of Wisconsin; and Kathy Hirsh-Pasek, from Temple University, and her colleagues.

The app should have a clearly stated objective and purpose. Will it help your child learn letters? Shapes? Colors? Numbers? Animals? AP calculus?

Information and lessons must be meaningful and relevant to the child (otherwise, honestly, what’s the point?). For example, if a game is teaching about shapes, it should go beyond simply identifying a triangle among a bunch of circles and squares. Instead, it should point out how various shapes show up in the real world (square and rectangular windows and books, round balls, holes in toilet-paper tubes and wheels, triangular trees, and so on).

The app should require active involvement. I’m not talking about physical involvement, such as swiping or poking, but mental involvement: thinking through how to solve a puzzle, figuring out what steps to take to help a character navigate its way out of a maze, or moving objects around on the screen to make two groups of the same number of items.

The app should be intuitive. (Your toddler isn’t going to sit down and read a manual.)

Your child should be in control of what happens in the app. For example, your child —as opposed to you or some other adult —should be the one to help the bunny find the carrot.

The app and the environment must be engaging and distraction-free. A lot of apps start with a story, and that’s great, because it’s easier to remember what happens in a story than a collection of random facts. Too many apps, however, interrupt the story with games, ads, pop-ups, music, animation, and other stuff that diverts the child’s attention from the key lessons. But interactive features that help move the story forward can be helpful, says Heather Kirkorian. Studies suggest that lots of distraction at this age may be associated with attention problems by age nine. At the same time, having TV or music on in the background is also a distraction that may draw the child’s attention away.

The app needs to be in the “Goldilocks Zone.” If it’s too easy, your child will be bored; too hard, and she’ll be frustrated. Either way, she looks away.