It is best if you do not volunteer at a centre that you are currently using to see your children. This is likely to be considered a conflict of interest. We would advise that you make your most of the time you have there with your children and make sure they are getting the best you can offer for the time being.
In the future it is beyond doubt that you will have an amazing range of experience that would be invaluable to a centre. On this basis, you might want to consider volunteering at a centre once you are no longer using this.