In the UK, there are farms with fields of pumpkins which allow you to go and choose the perfect pumpkin for your design idea. Simply Google search 'pumpkin farm/patch near (enter location)'
Prepare your surface with a sheet and something to collect rubbish in, as this can be a messy job
Cut off the crown (top couple of inches) of your pumpkin and put it to one side
Use a large spoon to take the innards out of the pumpkin. You can make use of the seeds by cooking them if you wish to
Use a small marker pen to draw the face on your pumpkin that you would like to carve out
Use a serrated knife to carve around the lines you drew, pointing the knife away from you to be safe. Children may need supervision with this task, or you can do it for them depending on what is appropriate
Put a few tea lights inside! The crown can be returned to the top of the pumpkin and taken off each time you want to light the candles