Hi there!! My name is XXXXX XXXXX am a licensed psychotherapist and certified teacher; I hope to offer you some assistance with your question tonight!
One really neat idea I have used in the past is "Operation Gratitude": this is a fantastic program where they accept leftover Halloween candy for soldiers who are serving overseas! Here is the link: http://www.operationgratitude.com/tag/halloween-candy-give-back/ It can be a fantastic project to take on as a family, or even as a neighborhood--- the kids can all choose 50 pieces of their candy to keep and 50 to give to soldiers along with a drawing or two; the attention is then off the candy... and on giving!
There are also some nursing homes, etc. who would LOVE to have some candy for their staff or residents, and it will turn the extra candy into a service project to teach the joy of giving to kids. Keep in mind that getting special treats on such a day is one of those things that makes childhood magical, so try not to force the issue to sadness on the part of the kids--- but if you make the plan ahead of time and have a special "sharing" box ready for the big day, you can agree to do the sorting before any eating, and you will end up with less candy, and a fantastic lesson to remember for the kids!
Otherwise, I would suggest that you allow a couple of small pieces per day until it is gone, and depending on the age of the children and the fact that you most likely encourage healthy eating year-round, they may even suggest what they think is a fair portion size to enjoy!
I hope that these suggestions were helpful to you; if not, please let me know and I will work with you on some more suitable ideas for your family. Thank you for your question--- and it is refreshing to hear the great care you are providing for your little ones! Let me know if I can be of any further assistance to you, and thank you for using Just Answer!! :-)