Just after 8pm I left my friends' house a happily married 33-year-old dad. By 9.17pm I was sitting in an ambulance on their street, a widower, in shock. I only remember the time because I noticed that the hands on the clock were in the same position as when our son was born two years and three weeks before.

My son and I managed to narrowly dodge the car that killed the woman I'd loved for the last eight years, the woman I'd married just the year before. It killed a wife; a daughter; a sister; a friend treasured by so many. But perhaps worst of all, it killed a toddler's beautiful, devoted mummy.

Jackson was at his mother's funeral but I don't think he had any idea what was going on. By this time I'd learned from a child bereavement charity that a 25-month-old can't grasp the concept of death. I'm sure that he did notice her absence from one day to the next because he would often squeal with excitement when he heard a key in the door, yet it wasn't until after the funeral that he really started to show any noticeable signs of missing his mum.

After she was killed, Jackson walked my dad to our front door and pointed at a light shining through the frosted glass. "It's Mummy," he told his granddad. And I suppose we all wanted it to be so – that her spirit had come to visit her son – but really I think that it was business as usual in my son's little head and he genuinely expected her to come home as night fell.

His apparent lack of heartbreak over the extended absence of his mum crushed me. Our home had been full of people calling her Desreen and not Mummy. So he joined in; within a matter of days he'd gone from calling her Mummy to Desreen too. It was like a dagger through my heart because I thought he was forgetting her.

Then something happened that brought me back to my senses. I put on a DVD, a show he hadn't watched in weeks, and he recited all the characters' names. I realised then that he couldn't have forgotten the person he idolised the most; he was just copying the big people.

Even so, it took about a month for Jackson to actually ask for Mummy in my company. Waiting so long for him to start to question her absence was the single most painful thing I ever felt as a bereaved husband, and the pain was for my wife rather than for myself. Sure, he'd stood at the front door and shouted her name when he thought she was coming in from work, but he hadn't yet asked, Where's Mummy?

When he finally did, he probably couldn't have chosen a worse time. He did it in front of Desreen's father, brother, and one of my close friends.

"Where's Mummy? Where's Mummy? Where's Mummy gone? Where's Mummy gone? Want Mummy. Want Mummy. Want Muuuuuummmmmmyyyyyy!" he cried.

He had been storing it up and now he was using it all in one go, and the men present unanimously did that thing where you think if you can tense your shoulders hard enough, you won't be in the room anymore.

The weight lifted off my shoulders and was transferred straight on to theirs. For me it meant that it wouldn't be long before I could finally tell him the truth about what had happened; for them it meant they were sitting in the middle of the one situation that they had dreaded most and didn't know how to deal with. Who the hell does?

Although he had now started to ask questions, that night would not be the moment he was told he'd never see his mummy again. He was already too distressed.

The right time came soon before Christmas. I'd taken Jackson to see my parents and family. The night after we arrived, I took Jackson to bed while he was happy and calm. I lay with him, read him a story and told him how much I loved him. He cuddled up to me softly. I realised that the time was right to start trying to explain.

As soon as my son had started asking where she had gone, I’d made a decision about how to handle it. I decided to tell him the truth. The illustrated books I'd been given, which explained to a badger that his elderly rabbit friend had gone to the stars, were not going to help my child understand why his mother would never be back.

So that night, the week before Christmas, I showed him a picture of Desreen on my phone and invited him to kiss it. "Jackson," I began, "Mummy's gone away and she can't ever come back."

"She didn't want to go," I continued. "She would never have left you out of choice because she loved you more than anyone or anything in the world. But Daddy's still here and I'm going to look after you now. And I know how to look after you because Mummy taught me."

We lay together until he drifted off. Once he was asleep I gently peeled him off my chest, tucked him into bed and went back downstairs to tell my mum what I'd told my son. I asked her and everyone who cared for him to use exactly the same words as I had, to try to minimise his confusion. I banned expressions such as gone to a better place because I worried that he might want to go there too or, perhaps worse, think she'd chosen that mysterious place over him. And I chose not to talk about heaven because, at that time, he didn't know the geographical difference between paradise and the local park.

The maddening thing about bereaved toddlers – or rather, any toddlers – is that you can tell them something one day but they may well have forgotten the next. Even if they say they understand, you can often find ways to prove that actually they don't.

The fascinating thing, though, is that he never really asked "Where's Mummy?" after that night. The question quickly turned to the statement "Want Mummy." His question had been answered.

He proved to me that he had absorbed the information just four months later. "Where's Jackson's mummy?" a friend’s three-year-old asked. The adults froze. But Jackson, a child 31 years our junior, replied, "She's gone away in the sky, far away. She can't come back." Then he continued to play with his trains.

Although I felt sad that he had to explain why his mum was no longer with us, I was also so proud of everyone who'd had a role in delivering a consistent message to him. Sure, heaven came into the equation for some people, "the sky" slipped in when it wasn't quite the message I'd originally briefed, but the important thing was that my son, who was not yet even two-and-a-half, could answer for himself.

But questions weren't the only thing that hurt; sometimes Daddy just wasn't enough. When Jackson fell over he would call "Mummy!" Whenever he felt sad he did the same. It's beyond painful to hear your child cry for something, for someone, you cannot provide.

Yet over time the mentions of her name would become a great comfort to me. Yes, Jackson would be distressed when he called for my wife, and perhaps it sounds strange that I could draw any solace from his suffering. But to me it meant she was still there in his head or his heart; that his reflexes immediately responded with a desire to be with Desreen.

Someone who worked at the bereavement charity once said to me, "He might forget the memories but he'll never forget the love." That’s a wonderful thought to hang on to when a child loses a parent too soon.

This is an edited extract from It's Not Raining, Daddy, It's Happy by Benjamin Brooks-Dutton. Learn more at lifeasawidower.com.