If you haven't seen your first holiday decorations of the season yet, they're not far off.
Holiday season is often the time when parents think about helping their children develop charitable instincts. It's a noble goal, but turning children into philanthropists is not so simple.
Some seemingly obvious moves to create charitable children have surprisingly little effect. And some can actually backfire, according to Joel Berg, executive director of New York City Coalition Against Hunger.
(Read more: How to give without giving headaches)
Take soup kitchens. A family outing to serve meals to your needy neighbors, especially around a holiday like Thanksgiving when many people are planning elaborate meals, seems like it ought to go a long way toward teaching charity.
Guess again, Berg says.
"The 7-year-old is making more work for the agencies," he said. "They're too young to move stuff around, and they can't really be around anything hot, or knives. The time it would take to instruct them is more than it would take for an adult."
That's not the only problem.
"Even very young kids have a built in b.s. detector," Berg said. "If you send them to a food pantry or kitchen on Thanksgiving that normally has 10 people volunteering, and there are 55 people there, they're going to see in a heartbeat that there are people standing around and doing nothing, and they'll get cynical."
It's better, Berg says, if kids participate in community service that aligns with their abilities and has a clear effect. For example, kids can lobby for funding for school breakfasts for low income students, writing letters to elected officials and talking to their school principals. Berg says he has seen children in a Newark, N.J., school delivering breakfasts to classrooms.
(Read more: More kids risk going hungry when school's out)
"A young person helping out with that could probably feed a heck of a lot more people," he said.
Talking to children about giving is also an extremely effective way to encourage philanthropy at a young age, according to a new study by the United Nations Foundation and the Women's Philanthropy Institute at Indiana University-Purdue University Indianapolis.
Debra Mesch, director of the institute, said the research showed that talking to children about giving increased by 20 percent the likelihood that children would give. That held true across race, gender, age and more.
"Role modeling in terms of household that actually give to charity isn't enough," she said.
A discussion of specifics is especially effective, Mesch added. "Saying you need to give to your church because it's your duty, or give to this organization because it's the right thing to do, that doesn't work," she said. "What works is, 'You need to give to this homeless shelter because these people will be happier when they have food in their stomachs.'"
The Rev. Barnaby Feder and his wife, Michele Lowy, used a variant of the talking method to help their children become charitable at young ages. Lowy, now a literacy specialist at Bristol Elementary School in Bristol, Vt., first thought of her method after reading an article in a parenting magazine when her children were young.
(Read more: Rich Give Less, But May 'Invest in Solutions' More)
Every year, beginning in October, Lowy and Feder, now minister of the Champlain Valley Unitarian Universalist Society in Middlebury, Vt., would start collecting charity solicitations that arrived in the mail. Then on the Sunday after Thanksgiving, the three Feder children and their parents would get together and go through the charities. Each child would be given $50 to allocate as donations, and each one had to be accompanied by a letter from the young donor.
"As they got older, they really took it on," Lowy said. "They had opinions or they would notice things in the news and say, 'That's a good thing to give money to.'" The children also developed favorite causes: Mattie, the middle child, regularly gave to children's cancer research after a classmate died of leukemia. And sometimes the charities—typically the smaller ones—wrote back with personalized thank you letters, which would make it more meaningful.
The tradition also had a positive side effect, Feder said. "I think it made them aware at a younger age than some kids that some organizations are more effective than others. We taught them to look at the percentage of money that goes to the cause." One year, after Doctors Without Borders won a Nobel Prize, Feder recalls that his son Linus declined to donate, reasoning that the prize would give the organization plenty of publicity—and new donors.
Feder and Lowy's children are now in college or beyond, so the tradition has faded. But they believe it was a winner.
"I think it has to be part of a whole approach to what it means to be a member of society," Lowy said. "But I think it makes a statement to the kids about what you think is important. It's one more statement that you make to them about being a good person. And it's an active statement."
—By CNBC's Kelley Holland. Follow her on Twitter