Families with babes in arms, and toddlers through to teens took part in the protest opposite the Syrian embassy in Belgrave Square, many bearing banners and placards.
Louise, 41, mum to Sam, 4, and Mungo, 17 months, told the crowd how devastating images of slaughtered infants had driven her to organise the demonstration, with the support of her partner Jim, 45.
Youngsters wearing the names of 49 of the children massacred in Houla on May 25 placed red roses in their memory on the railings opposite the embassy. The names of the dead were read out, before the demonstrators sang 'Rock a-Bye Baby', in tribute, said Louise Tickle, to those children who would never again have a lullaby sung to them.
One protester, Annemarie Key, took two of her three children to the demo, telling us she felt it was 'abhorrent' what was going on in Syria:
"How can anyone sit back and let it happen? I don't normally take a stand but seeing images of those innocent faces made me weep," she said, "I heard that this protest was specifically for families and brought my boys because it's the very least I could do."
She told us she had explained to her older son, Leo, 10, what the protest was about, but had simply told her four-year-old, Ronan, that the children had passed away: "Ronan is a bit young for full details, but he did know children had died. He said to me: 'So their mummies won't ever see them again? That's sad isn't it mummy?'"
Fellow demonstrator Sian Lewis had travelled to London from Sussex with her partner Andrew Lark and their baby daughter Madeleine. She told us she had been inspired to join the protest after hearing Louise on the radio.
"I have never demonstrated before," she said, "but as a mother, the thought of someone taking my daughter out, binding her hands, slitting her throat... I had to do something. I thought my own mum would be against me taking Madeline, but she actually said 'good for you'."
Joshka, a mum of two from Sweden said she had lived in Syria from 1997 to 2002 and that it was her 'dream' to take her own children, aged four and six, there.
"It is a great country but with the wrong government," she said, "I had the best time of my life when I lived there, and it is from the heart that I am here. I have lost friends in the last weeks and I am devastated. The Syrians are the most wonderful people."