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The crowdfunding platform Kickstarter has announced that its employees will work four days a week starting in 2022, and the pandemic is reshaping workplaces across the country. “Is a Four-Day Week the Future of Work?” a headline in this newspaper recently asked.

Let’s hope not. Despite the hype, four-day workweeks have drawbacks if they mean longer workdays. Companies may say that working hours won’t increase, but reality can be different from what is outlined in a corporate handbook. This is a particular problem for families with young children.

For many parents, cramming five days of work into four will mean less time with their children. Three-day weekends can be great for bonding, but children need a consistent, daily presence, not occasional chunks of time. Shorter days, not fewer days, are preferable.

The needs of children are best met when they spend time with their primary caregivers every day. Four-day workweeks can provide parents with the illusion of presence because they are available in large blocks of time during the weekend. But if this comes at the cost of barely being around during the week—missing bed time or homework after school—the long weekend won’t yield much benefit.

The idea that time quality is more important than quantity is a myth. Quantity of time is important for both toddlers and adolescents. Nicholas Zill, a researcher with the Institute for Family Studies, reports that a parent’s presence during adolescence significantly affects a child’s success, including overall educational attainment.

The presence of a parent increases trust and a sense of security. It is also how children learn to regulate their emotions and develop resilience. Columbia University’s Nim Tottenham has shown the importance of caregivers for development of the amygdala in very young children. The best scenario would be a parent who worked 9 a.m. to 2 p.m., with an option to finish their duties from home where they will have more time to be with their child throughout the day and at bedtime.

A trend toward shorter workweeks isn’t a bad thing. The search for alternatives to the traditional workweek—five days and 40 hours in person—is a great sign of progress for families with children. Companies stand to benefit: One survey found employers lose $300 billion a year in lost productivity from stressed out parents.

The pandemic has created new, flexible schedules that are almost certainly here to say. But what working parents need is a greater ability to focus on the demands of young children. Companies shouldn’t jump on the bandwagon of four-day workweeks without considering the hidden costs to families.

Ms. Komisar is a New York psychoanalyst and author of “Being There: Why Prioritizing Motherhood in the First Three Years Matters” and “Chicken Little the Sky Isn’t Falling: Raising Resilient Adolescents in the New Age of Anxiety,” out in October.