You may not be able to do anything but accept that fact. Just because the activity is a worthy one doesn’t mean that your children will find it (a) interesting, (b) something they are willing or able to make time for, or (c) turn them into mini-philanthropists in their own right. And if wails of "Mom always liked you best!" echo through the hallways at family gatherings now, don't expect that to change just because this is a "good deed" activity.
I've worked with dozens of donors who set up their foundation with the primary goal of forcing, er, providing an opportunity for their children to work together in order to build strong family bonds. It's not always that simple.
There are several things that can help. Most of them require that you, the donor, cede decision-making power to your children. Yes, I know that can be difficult for donors. But if your children's involvement is most important to you, it's a step that must occur.
First, if possible, bring on all your children. Showing favoritism can lead to major issues. Additionally, if the board of directors of the family foundation consists only of you, your spouse, your long-time financial advisor and and your attorney, asking an 18 year old or even a 30 year old to hold their own in a discussion among such old fuddy-duddies is asking a lot — unless you provide them with a cohort that can amplify their voice. To address this try to bring on more than one younger generation trustee at a time.
Second, be flexible.Your children (or grandchildren) are busy trying to get their start in life. And they may not have the ability to take time off work for a meeting during the week — or afford a babysitter for a weekend. Schedule the meetings to make it easier for their schedule rather than yours and if there are costs involved (travel, etc.) that are a hardship for them, consider covering their expenses.
Third, be sensitive to the time crunch. Younger folks with children or exams have much less time available for outside the home activities. Allow them to take time off or elect to serve or not each year and still come back the following year. If board service becomes a burden and you make it clear that you believe your children aren't pulling their weight, you'll risk losing them completely from the foundation's activities. And you'll appreciate the leave policy when you need that hip replacement or long vacation!
Lastly, jointly make a decision about how you'll make decisions. It is very common for everyone else on the board to defer to the matriarch or patriarch. Give the next generation an equal say in what the foundation funds, which criteria it uses to make choices, and how it evaluates its successes and failures.