KS3/4 children can struggle with the concepts of current and voltage, and with how to correctly connect an ammeter/voltmeter. I tried this analogy: current is like the number of children running through a corridor /sec: Mr Amp (the ammeter) stands in the corridor counting children (electrons) and timing them (this explains why the ammeter is wired in series). This can help in showing conservation of current around the circuit and explain observations in parallel vs series circuits. Also contains a slide of investigations to complement it.
See also: Mrs Volt (chocolate biscuits and voltage)!