Attention span varies according to the conditions the person is in and what the person is concentrating on. For instance, the more television a child watches and the more video games a child plays, the less they'll be able to concentrate on reading.
In general, attention span increases with age. A two-year-old may have an attention span of 1-2 minutes, while adults can have spans of 20-30 minutes.
The American Academy of Pediatrics recommends that parents of children under the age of 2 should not allow their kids to watch TV, including educational DVDs. Pediatrician Dr. Dimitri Christakis has done studies on the detrimental effects of TV on children's attention span and offers suggestions on how to make the most of TV and technology in his book "Elephant in the Living Room".
To increase your child's attention span, expose them to more outdoor activities and social playing. Reading to your child is another great way to improve their attention span. Having them learn an instrument or spending time listening to music are also great ways to improve their concentration. And ensuring they have a good night's sleep with regular bedtime hours will also help.