Do a costing of how much they really cost to make, or would have cost if you had to go out and buy all the materials new. at shop prices. Then time how long it takes you to make them (If you do them on a "conveyor belt" system, then make a batch and divide the time it takes to find how long for each, and work out how many you can make in an hour) and add enough for the minimum wage, which at the moment is £7.83 an hour for over-25s. (If you were doing this as a manufacturer, you would then add on the costs of overheads - which people who are making crafts for pin money often forget about - rent, heat, insurance and so on)
Don't under-price your work! People don't actually value the things they get very cheaply, and remember that your objective is to raise money for the charity, not to provide ultra-cheap stocking fillers for buyers. If they don't sell fast enough at your costing, you can always reduce the price, or quote a cheaper price to children obviously buying presents.
If you are not getting enough for things to cover the cost of the materials plus something extra for the (valuable) time you are spending on them, you would be better to not make anything but just hand over what you would have spent on all the bits and pieces. Not so much fun, though.