Disclaimer: I don't own Torchwood and I'm not making any money from this.
Timing: Sometime around Season Two, although refers to information revealed in Children of Earth.
Jack's Children
There was no one alive who knew that Jack Harkness had three children. Not even them.
The first was with Lizzie, the only person Jack had ever formally committed to. Jack had met her in a dance hall in Cardiff, on leave from the front in World War I. He'd never believed in love at first sight until he'd fallen head over heels into it. He'd spent the whole evening by her side, walked her home and told her he was coming back the next day to ask her father for permission to marry her. She'd laughed, until he'd done exactly that.
Her parents had been less than keen at their daughter getting engaged to a man she'd met less than twenty-four hours ago, but had come round. Firstly, because it was wartime and people did that sort of thing. Secondly, because Jack was a 'good catch' for their daughter, who came from a very modest background and – for reasons Jack couldn't fathom – was considered a poor second to her older sister. And thirdly because Lizzie threatened to run off with him to Gretna Green if they wouldn't give permission, and the look her parents exchanged suggested that they thought she would actually do it.
He'd had to go back to the front a few days later, but not before they'd booked the church and the reception venue and had an impromptu engagement party with Lizzie's friends and neighbours. Jack had bought her a diamond ring and kissed her goodbye on the same day.
They'd married, as promised, the next time he'd managed to get leave. After a blissful week together in a small hotel, he'd had to go again.
He'd been ecstatic when Lizzie had written to say she was expecting and had told precisely everyone he'd come across in the next few days. He'd managed to get home when Lizzie was six months' pregnant and had marvelled at the way her stomach moved. He'd lain awake for hours at night, his hand on her belly, feeling their baby kick. Vowing to be the best dad he possibly could.
He'd known something was wrong when he got the letter with her mother's handwriting on it. Lizzie had been suddenly taken ill – with eclampsia, he later found out – and she and their son had died.
When he had first seen Gwen Cooper, he'd felt a flash of recognition. Delving into her family history, he'd confirmed what he'd suspected: she was a descendant of Lizzie's. He could see it in the curve of her lips and the shape of her ears and... well, a lot of things. There were times when he looked at Gwen and had to give himself a mental slap so that he remembered she wasn't the woman he was seeing. It wasn't as if they had the same personality. Lizzie had been... well, if he was honest, a lot like Ianto. Smart, sarcastic, neat as a pin, fantastically organised. Very proper in the outside world, but passionate behind closed doors. It was her nature to take care of him and others and strangers might have thought her submissive, but she was perfectly willing to take charge, or tell him that he was being an idiot.
In fact, they had a shit load in common. But he probably shouldn't tell Ianto that. Jack knew full well that Ianto hated being labelled 'the girl' in their relationship, as everyone seemed to think. Jack didn't really understand labels anyway, but that one in particular mystified him. Surely the best part of being with another man was the ability to switch roles depending on your mood? Why in the Doctor's name would he want to pick just one?
His second child – another son – had been born to a fellow Torchwood employee named Mary in the 1940s. Their affair had been brief and volatile, but the pregnancy had seemed to settle things down between them. While Jack wasn't at all sure it would last, he was determined to be there for this baby. When little Jack was born, he had been overwhelmed with love for the tiny, red-faced, squirming little bundle. Every moment they spent together made Jack feel that it had been worth living so long and dying so many times, just to get to this.
When little Jack was three weeks old, Mary had left him. In her note, she wrote that she couldn't expose her son to the dangers of Torchwood – or the dangers of Jack Harkness. She wasn't coming back and he shouldn't try to find them.
He had. He'd searched everywhere and everything, madly frustrated at the limits of technology available to him. Eventually he'd tracked them down, in America. He'd undertaken the long journey, finally arriving in their town worn out and desperate to see his son. Only to find that they'd both died in a car crash only a few days before.
Then, in the 70s, there had been Lucia. She hadn't even waited until their daughter was born to leave him. She'd gone into deep cover and he hadn't been able to find her. Alice had been an adult by the time he'd managed to track her down. Lucia had died by then, but her legacy lived on. Alice agreed to see him, but she didn't trust him. He didn't think she ever would. Even his own grandson thought he was his uncle, although Jack realised the truth would have been difficult to explain.
After that, he'd pretty much sworn off women. Things had changed enough that he wasn't going to get thrown in jail for sleeping with men (he didn't want to repeat that experience) and – in this century at least – he could be damn sure they weren't going to get pregnant.
No more children. Three was enough.