Ms. Kondo strongly encourages parents to include children in the task of folding laundry. “Like reading a book, it’s a habit to fold clothes with my children,” she said. Children mimic their parents’ tidying tasks, and even when their work needs to be redone neatly, they enjoy being involved.

Getting children involved also means respecting what belongings make them happy.

If your kids balk at your attempts to declutter their belongings, you can still keep those things neat and accessible with affordable, collapsible bags and bins like the ones we recommend in our guide to toy storage.

Erin Boyle, author of “Simple Matters: Living with Less and Ending Up with More”and founder of the lifestyle blog Reading My Tea Leaves, lives in a one-bedroom apartment with her husband and two small children. Ms. Boyle encourages her 2-year-old and 4-year-old to participate in tidying by giving them straightforward, visible storage like wooden crates that live under the bed, a kid-level bookshelf, and low-hanging hooks for their coats. When artwork from school starts to pile up, she asks her children to help decide which pieces are ready for the recycle bin. “I have one little cardboard box that we keep for their favorite drawings,” she said.

Ms. Penn and her 22-month-old daughter sing a song and turn toy tidying into a game. “I find that when you can empower kids, they want to help out,” she said.

Belongings that have meaning can’t spark joy when they’re boxed up in the garage. Instead, Ms. Kondo encourages her clients to decorate with their photos and sentimental items so they can enjoy them every day.

With physical photos, she recommends applying the same level of intention as with every other category in the home. When looking at similar photos taken at the same sitting, she says, choose the photo that sparks the most joy and toss the others. Ms. Kondo encourages her clients to put photos into an album that can be displayed and enjoyed.

If most of your family photos are digital, declutter your photo files and create a photo book for the coffee table with the best of them. We recommend Shutterfly Photo Books, which offer high-quality photos and customization options at a good price.