This problem is a little more difficult than it looks. It requires children to visualise the adjoining faces of the cube and transfer this to a net of the cube.
You could start by showing the group the problem on an interactive whiteboard or data projector. When you have discussed it and what needs to be done children could work in pairs so that they are able to talk through their ideas with a partner. They could use a print-out of this sheet or draw the faces of the cube for themselves. Scissors and sticky tape would be useful!
When they have built the cube they should then transfer it to a net. This can be any arrangement which can be folded into a cube not necessarily just the conventional cross given on the sheet. At the end of the lesson, the children could show the whole group both their cubes and the nets they have drawn. The class' work would make a great display, along with a copy of the challenge itself.
Why do you think these two faces are next to each other on the cube?
Look at these two faces. Which other one goes near them?
Those who found this task straightforward could try to make the net of the octahedron from this sheet.
Suggest making a net from this sheet and leaving it so it can be folded and unfolded. Then draw or paste on the faces one by one. If "Polydron" squares are available the cube can be built up using the pieces from this sheet.