There are literally thousands of websites about crystals, a quick search will bring you a wealth of information. Most children are naturally drawn to crystals and stones. Just playing with the crystals will make them feel better. It is important to cleanse crystals when you first buy them. You can either hold them under running cold water, use sound (putting them in a pan and banging it with a poon is fine or if you have a singing bowl you can use that) or place them in a bowl of salt. You should cleanse them regularly to keep them clean and sparkly.
Here is a list of properties to explain the most common uses for some of the most helpful crystals for children, but remember you know best what you need so if you are drawn to a particular crystal it is for a good reason.
Amethyst - Amethyst is a beautiful purple crystal. It is great for helping you fall asleep, it will stop you having bad dreams and is good for making you feel calm and friendly.
Rose Quartz - This is a beautiful pink stone which makes you feel loved. It is a wonderful stone if you are feeling lonely or sad, I can also help you to love and look after yourself and know how special you are.
Howlite - Howlite is a turquoise stone, it is a wonderful stone for helping you to communicate, to be confident enough to say what you need to with love. If you have to read out loud or tell someone something important Howlite will help.
Citrine - Citrine is a yellow crystal which is wonderful for making you feel brave, it removes fear and is also good for helping tummy aches. It is also good for hormonal changes as you get older.
Bloodstone - Bloodstone is a green and red stone which is very healing. It helps you feel creative but also protects you from negative things. It helps you have good dreams, gives courage and teaches you how to avoid dangerous situations. Bloodstone helps you to share and also helps you get used to new situations.
Clear quartz - This is a very popular crystal because it can be used for lots of different things, whatever you want this crystal to do it will and it will make other crystals even more powerful. It helps keep you well and helps you stay positive and happy.
Snowflake obsidian - Snowflake Obsidian is black with white snowflakes, it is calming and soothing. It teaches you to value mistakes as well as successes. It restores balance for body, mind and spirit and helps you with negative thoughts. It is a wonderful crystal if you are feeling lonely and is also very helpful when you are meditating.
These are just a few crystals which are useful for children there are some wonderful books about crystals.
If you would like to buy these crystals I have a Children's Crystal Set which contains all of the crystals above and a card with all of the information listed here available in my shop.