Nearly 2/3 of kids 12-15 in the UK have a smartphone, compared to 45% of adults

"Children’s access to the internet is not restricted to PCs or laptops. Those aged 12-15 are more likely than last year to go online using their mobile phones and are more likely to say that this is the device they would miss the most.
Since 2011, there has been a 50% rise in 12-15 year olds owning smartphone devices. Almost two thirds (62%) of this age group now has one – up from 41% the previous year. This is significantly higher than the UK average for adults of 45%.
Mobile phones are more important to this age group than any other device, even TV. Two fifths (39%) of 12-15 year olds now say they would miss their mobile phone more than any other device, up from just over a quarter (28%) in 2011. Only one in five (20%) said that they would miss TV the most.
Around one in seven (14%) of all children aged 5-15 now use a tablet device at home, a threefold increase since 2011 (5%). Children aged 12-15 are most likely to use a tablet, with 17% saying they do, up from 6% in 2011."

Source:  Data from Ofcom reported in a press release, 23rd October 2012

Note - Lots more data about kids & media use in the full release

Full report here