Is it true that parents favour one child over another? Does this mean that their parents love them less?

Yes but it's not so much having a favourite but more like showing love and affection in different ways. For my mom, her clear favourite is my younger brother. My elder brother and I used to detest this and we'd always call her out for being unfair. But as we grew older, we realise that she does love all of us equally but in different ways. For me, it was a little more strict because I was the only girl, for my elder brother who was rebellious, she practised tough love and for my younger brother, because of his age, she paid more attention to, which we saw as more love.