I recognized that my two children could use a touchscreen almost a year ago when they were 1 and 3 years old. When the iPad came out it was a no-brainer. Unlike a mouse, touchpad or keyboard, the touchscreen on my iPad is very usable (apps are a diff story) for my now 2 and 4 year olds and makes discovering computers a joy for them.
Yes they still go outside, get dirty and explore like any other kid. They just have this in addition to all that "real" stuff.
As a father of two young children, I kept them away from computers and screens as much as possible until they were 3 years old.
Babies are wired to be learning about and interacting with their physical environment and the lifeforms around them. Exposing them to highly artificial and abstract phenomena before they have developed the abstract thought processes to assign relevance and meaning to them seems to be at best at waste of hard earned neural circuitry, at worst developmentally damaging.
We need to be gently nurturing our children's imaginations not flattening it and rendering it obsolete via technology. There's plenty of time for kids to discover computers, but once they do other all the other things they love doing will have some serious competition for their attention.
...you mean stuff like stuff human speech, maths and other modern inventions?
However, I might want a sick proof case if I was letting a young child (say under 4) use it while traveling.