There are many different ways you can help children cancer charities. Here are some suggestions.
Donate a Vehicle to Charity
If you have an old vehicle (car, boat, motorcylce). You can donate it to a charity and receive a tax deduction.
Donate Money to a Cancer Charity
You can also provide money directly to the charities. To make sure your money is best spent please look into how the organizaion will spend your money. How much is spent on actual programs and how much is spent on managment and other overhead. Also you should look into if your company will match your donations.
Volunteering at Children's Hospitals
If you do not have money you can always donate your valuable time. Local hospitals are always looking for help. This is a list of hospitals across the country and their volunteer web pages.