Tablet and Smartphone use for children

With some jurisdictions categorically recommending that children under a certain age (in the case of Denmark under 13) should not have a tablet or smartphone, what is your opinion on the appropriate age/way to introduce these devices to your children's life? Do you use your own devices together with your children? If so, how and when?

While my own children are still unquestionably too young for tablets or smartphones, I'm already afraid of the social pressure that is likely to arise at an ever younger age when their friends start getting devices.