Remind the children of some recent activity at the school to raise funds for a charity. Or ask the children what charities they know of that are concerned with young people (Barnardo's, Save the Children, the Church of England Children's Society, etc.)
Ask what sort of events are held to bring in money for children's charities - sponsored swims, fairs, performances of plays, etc. etc.
Tell them that in the 1730s and 40s there were many orphaned or abandoned children in this country and that one man, Thomas Coram, set out to establish a place where those in London could be properly cared for. In 1740 he founded the Thomas Coram Institution.
This needed a great deal of money. On 1 May 1750 there was a very important fund-raising event there. It was a performance of a piece of music called the Messiah, which had been composed just a few years earlier, by George Frederic Handel. Tell them that, in fact, Handel was very generous. Although he was dependent on making money from his music in order to be able to live, he was always ready to put on performances for good causes and that when Messiah had first been put on, in Dublin, it was for the benefit of three charities.
Play an extract from the Messiah.