What can young people aged 13-16 do to get involved in politics?

[WomanInTheWindow]

My niece and her friends have been talking about the environment, Brexit, Iran etc as things come up on the news. Sometimes they say they wish they knew more about what they could do.

What would be a good starting point?

Try searching for your local youth council, eg Manchester youth council. Every area should have some opportunity for young people to become engaged.
There are then opportunities for becoming a member of the British Youth Parliament and both Wales and Scotland have their own youth parliaments as well. Dd was an MSYP and member of our local youth council for several years.