Jenny Bristol, Homeschooling Parent, Writer, and Editor
In my mind, there is a difference between outright giving a child a tablet, laptop, or other device and allowing them to use a family device. I believe that when small children are old enough to know about cause and effect and to be careful with such a device, it is perfectly fine to allow them occasional use of family devices for educational purposes, while you monitor their activity.
As for giving them one of their own, somewhere between 10 and 12 would be a good lower limit, depending on your needs and how responsible your children are. If you homeschool, your children would be more likely to benefit from having their own devices than if they went to conventional school. Certainly high school is a great age for encouraging kids' independence with devices for educational purposes, paving the way for them to have a good laptop for college. Help them by setting them up with useful utilities and applications, and bookmark some "approved" sites they can go to for research and other educational uses.
Be careful about "educational" resources found on the internet and for tablets, however. Many things are educational in name only, without actually teaching kids to think in new ways. Regardless of your kids' ages, preview apps and programs that they use, and also keep tabs on their internet usage. Don't invade their privacy, but it can be helpful to have them use their devices mostly in family spaces in the home.
Also, make sure that device usage is only a portion of their educational experience. Use digital solutions as an extension of their learning, a way to practice lessons in a different setting and to integrate technology into their new knowledge.
My best advice, however, is this: Know your kids. Will they be careful with technology? Will they be safe online? Will they be responsible with digital citizenship? When you can answer these in the affirmative, it may be time to give them their own device. Hand-me-downs from you are a great place to start. But be sure before you do this: You won't want to give them a device and then take it away. That will be much harder on them than not having the device in the first place.