I could hear them talking in the other room.

My wife’s voice was soft, nearly whispering. My son’s voice, on those rare occasions when he interjected, was uncharacteristically tentative, uncertain and wary. I stopped listening. I knew what was being discussed.

My wife has multiple sclerosis. And she was explaining it to him.

Mom and Buried had been diagnosed about six years earlier, not long after our first son was born. In the years since she first started visiting a neurologist and taking stock of her illness, her prognosis has worsened only slightly — from a diagnostic perspective.

On a day-to-day level, as someone who has to deal with the spasms, tingling, and numbness her illness brings, my wife has felt her symptoms progress in a way that seems to belie the MRI results, bringing more pain, more sleepless nights, and more slow mornings.

In the grand scheme of things, she has been lucky — or as lucky as someone with a degenerative nerve condition can be. But with a disease like MS, it’s not today that scares you. It’s the uncertainty of where you’ll be 5 years, 10 years, 20 years down the line that causes anxiety. It’s the unpredictability of the disease’s progression and where it may take you, where you may end up, or what your life will be like decades from now that worries you most.

It was with that uncertain future in mind that we decided to explain Mommy’s illness to our first-grader. Having recently welcomed a younger brother, it had been a tumultuous year for our eldest. While we knew he wouldn’t grasp everything we told him, we felt it was only fair to give him some context.

She wanted him to know that there was something else going on beneath the surface — something a 6-year-old couldn’t possibly guess at and that he probably wouldn’t even understand. Not entirely. Not at first. But it was important to us to reassure him that not every change in Mommy’s behavior was a result of the new baby.

Having a second child was something of a gamble in the first place, even without worrying about the shift in family dynamics, let alone my wife’s disease. There were so many unknowns.

How would my wife react to pregnancy? Would it take too much of a toll? Would her symptoms flare up? And that was only for the first 10 months. What about after the baby was born? He would be around a lot longer than her distended belly. Would caring for a newborn make things worse? Would she even be able to carry and nurse and chase a baby, a toddler, a preschooler?

It was 15 months since our second baby was born, and things were going okay. To his credit, our eldest understood that things would change when his little brother was born, and he was handling the transition from headliner to co-star quite well. But while a 6-year-old might intellectually accept the shift in dynamics, his emotions sometimes get the best of him, and there were tough moments. Mommy’s occasional inability to interact with him as much as he’d like — due to both baby care and her MS — has been impossible to ignore.

The attention we were able to pay our 6-year-old and the activities we were able to participate in with him were already being throttled back in service of the new baby. How much would my wife’s disease add to that discrepancy? How much might he resent us, her, or his little brother without knowing the full story? We didn’t want to take that chance.

Obviously, sometimes it is the baby’s fault. (No offense, kid!) Babies simply need more care and focus than 6-year-olds. My eldest can be independent in ways the baby won’t be for years. In that way, the five-year age gap between our two children has been helpful.

But even with that separation, there are simply days when the toll of managing two kids — one of whom is an infant — are worse than others. Recently, there had been more of those days. My wife had to cut short some of our 6-year-old’s treasured play-dates, and she’d opted out of several planned trips to the park. We didn’t want our son to get the wrong idea, so we decided to tell him what was going on.

What can you really tell a first-grader about something like MS? This is a disease that doctors don’t completely understand — a disease with a lack of outward manifestation that can raise skepticism in even the most sympathetic bystander. Not everything my wife experiences is visible to the naked eye; if she’s one of the lucky ones, not much ever will be. But the absence of obvious symptoms complicates a challenging discussion with a child who already can’t — and shouldn’t be asked to — grasp the reality of his mother’s illness. Still, we felt he deserved an explanation.

“No, Mommy isn’t too focused on the baby play with you,” we explained. “No, Mommy doesn’t love you any less. Mommy is sick. Mommy gets tired. Mommy wants you to know that it’s not you, but sometimes she can’t do the things you used to do together. Not all the time, at least.”

So she sat with him in his bedroom, and she told him the truth. Not all of it. Not the details of her medications or the worst-case scenarios — but enough to include him and to hopefully assuage his fears and insecurity. She told him about her MS to offer him reassurance and also to ask for his help when she needed it. He understood, in that surprising, intuitive way that children always seem to. He understood and he hugged her, and then he got back to playing with his LEGO set.

Will it take? Maybe. Maybe only sometimes. But sometimes is enough for now. He deserves to know, and we needed to tell him. She needed to tell him.

My wife and her firstborn have a very special relationship, and she may not express it often, but I know she fears that her disease may fray it. Reassuring a child that a new baby won’t change things — not the big things — is one thing. Explaining to a 6-year-old that your “invisible” illness won’t change things is another. There will surely be more conversations about multiple sclerosis in his future — and in his brother’s, as well. But it was time to lay the groundwork, to rip off the Band-Aid for both my son and my wife.

Parenting is full of such challenging conversations that you don’t want to have, you wish you didn’t have to have, and you didn’t know how you could ever have — but they’re conversations you ultimately find a way through.

And then you move onto the next one and the next, and you hope something sticks.

(illustration by Erica Root – Find more of her awesome work at her website and on Instagram)

A slightly modified version of this post originally ran on Care.com