It is easy to get started, all you got to supply is about 60 ml of cold water and a mixing bowl and spoon (plastic recommended). You will also need a pair of scissors to open the packets.
The instructions tell you to mix water into the plaster. This is wrong! You must always put water first and then sprinkle the plaster on top. Once it's wet, you gently stir the mixture and pour into the mould. If you do it the way they suggest, your mixture will have lumps in it and be brittle. After you pour the liquid plaster into the mould, do not forget to tap the mould on the table to help the air bubbles rise to the surface.
When the plaster is cold and has hardened, you can turn out the mould onto a towel. Break any extra plaster around the figurines with your thumb. You can smooth the edges with fine sandpaper if you wish but I am sure the kids will be eager to start painting. Advise them to start with the lighter colours first and let each layer dry before they proceed to the next. You will need to mix the paints for them in a palette because at a younger age they are not able to do this successfully. Protect their clothes and surfaces as the paint is not washable (no matter what they claim). The amount of times that strip of paint tubs has dropped on a carpet or overturned on the table... It takes increased manual dexterity and colour sense to produce figurines as beautiful as the ones pictured on the package. Some children may find using felt tip pens easier than using the brush as it is miniature work.
Now to a bit of criticism to the product:
1) the moulds are not detailed enough
2) the plaster is not good quality. It is not Plaster of Paris (the white one which gives a really smooth and pleasant finish).
3) the pins are fiddly to insert so wait till the mixture has thickened (but not fully set) before you insert the pin and hold it till the surface hardens or it will drop into the mixture and be unusable. I don't like the pins and anyway the figures are bulky to be used as badges.
But the positive thing is you can reuse the mould with some Plaster of Paris (buy it at any Craft shop) and keep experimenting. Craft shops also sell magnets.
PS: to clean the bowl used to mix the plaster, wait till the remnants have hardened and then give it a bash against a hard surface and the pieces will come off easily. For environmental reasons and to save yourself from pipe blockage, do not pour powder or liquid plaster down the sink!