Most parents would do anything to make their kids happy. But sometimes, you simply can't give your child exactly what they want in a given moment — and that's a good thing, according to a child psychologist.

"Saying 'no' to our kids is an important way of showing them that we love them," Becky Kennedy, a Columbia University-trained child psychologist, said on a recent episode of her parenting podcast "Good Inside."

Parents who say "yes" to their kids too often— whether reflexively or as an attempt to avoid tantrums — actually do their children a disservice in the long run, Kennedy said. By giving in too easily, you can inadvertently damage necessary boundaries that help children learn appropriate, respectful behavior, she added.

"Yes, it's important to help my kids feel like their wants and needs are valued, and that is actually independent from saying 'yes' or 'no' in any given situation," said Kennedy. "In fact, I would argue, it almost becomes dangerous for our kids to conflate being valued with getting what they want."

DON'T MISS: The ultimate guide to earning passive income online

The discomfort of being told "no" helps children learn to cope with disappointment and develop patience, Kennedy said. Kids who lack those traits may struggle to develop the ambition and motivation they'll need to be happy and successful as adults, research shows.

Kennedy, a mother of three, noted that her own kids also "freak out" when she denies them something they want, but can't have at that moment. Hold firm and stay consistent, she advised: If you "pick your battles," you'll probably end up saying "yes" more often than you'd like.

"At times, I struggle with this too," said Kennedy.

But any parent's two biggest jobs are setting reasonable boundaries for your children, to keep them safe and teach important life skills, and validating their feelings to build trust and help them learn how to regulate their emotions, Kennedy said.

Considering each difficult "no" as an accomplishment, rather than something to dread, can make it easier, she noted. Whenever your child reacts negatively, move onto your second job — validating their feelings — by listening to them and offering support. That part "often comes down to three words: 'I believe you,'" said Kennedy.

Then, go back to your first job and reinforce the boundary. The simple, repetitive process helps build trust and sets expectations for children, all of which aids their emotional development, Kennedy said.

The process is "hugely important for adult life skills," she added. "Because if we conflate feeling wanted and valued with getting what we want, we actually set our kid up to be fairly entitled in the world. And that's not what we want."

Want to make extra money outside of your day job? Sign up for CNBC's online course How to Earn Passive Income Online to learn about common passive income streams, tips to get started and real-life success stories.

Plus, sign up for CNBC Make It's newsletter to get tips and tricks for success at work, with money and in life.