Children can understand charitable giving and helping others. No age is too young to start.
With your kids of all ages, get them involved. Create a change jar for giving to charity. Each month or so decide as a family where to donate the money. Then, if you want, roll the change or take it to the bank for counting with your child. Writing a check is great but taking the money to the charity together is a tangible lesson. Children learn in all ways including seeing and experiencing the location and people you are helping.
Some families donate time together. They go and work at homeless shelters providing holiday meals or make it a monthly time to support their favorite charity. Making it age appropriate to your children is a perfect hands-on lesson.
My grandmother you to hand me a dollar to put in the basket at Sunday Mass. Yes, this was a start of a lesson. However, the more intentional and planned and discussed donating is, the better the long-term outcome.
Yes, as a parent you have plenty on your plate. Teaching your child about charitable giving is a two for one accomplishment. You are teaching your child about your values and helping others. Plus, the giving circle will continue as they practice in future years the giving that you taught them.
Remember, the dollar amount does not count as much as the action. The attitude of gratitude is enhanced with giving.