Children and Parents: Media Use and Attitudes came out in October, and has masses of data on how British children are getting their entertainment across different devices.
And it have nice information about kids:

This reduction in ownership of mobile phones that are not smartphones comes at the same time as a sharp increase in the use of tablet computers at home, which has tripled among 5-15s since 2012, and a decline in TVs, radios and games players in children’s bedrooms.
Four in ten (41%) 12-15s with an active profile say they mostly use a mobile phone to visit their main social networking site profile - which makes this the most popular device for accessing their profiles.
Smartphone users send an estimated 184 instant messages (IM) in a typical week and smartphones are the most popular device for accessing social networking sites among 12-15 year olds.


For the first time there has been a decrease in the number of children with social networking profiles, and there appears to be greater diversity in the types of social networking sites being used. However, there has also been an increase in the number of children who can potentially be contacted by people unknown to them via their social networking profiles. Parental awareness of the minimum age requirement for Facebook has increased among parents whose child has a profile on this site.
Most parents of 5-15s say that they know enough to keep their child safe online, but around half of parents continue to feel that their child knows more about the internet than they do, as do 14% of parents of children aged 3-4. This may reflect the fast pace of technological change and the ease with which younger children in particular can embrace and explore new mobile technology and apps, and suggests that parents need continuing support to build their own skills and confidence.
Tablets are becoming the must-have device for children...
Around one quarter of children aged 12– 15 (26%) and 18% aged 8-11 have their own tablet computer, while household ownership of a tablet has more than doubled since 2012 (51% vs. 20%). Use of a tablet computer at home has tripled among 5-15s since 2012 (42% vs.14%) while one-quarter (28%) of 3-4s use a tablet computer at home.

...while older children opt for smartphones...
Ownership of mobile phones among children aged 5-15 has decreased to 43%. This is a decline of 6 percentage points since 2012, driven by a 10 percentage point decline in ownership for 8-11s (33% vs. 43%) and a 5 percentage point decline for 12-15s (82% vs. 87%). However, smartphone ownership has remained stable for 8-11s (18%) and 12-15s (62%).

Among 12-15s, schoolwork/ homework is the most commonly-mentioned internet activity (84%), followed by information (79%) social networking (68%) and watching audiovisual content (68%). A majority of 12-15s also go online weekly for other communication (66%) for games (54%) and for music (53%).
And about tariff....

Personal information for sharing...