We're onto you, parents: It turns out you do have a favourite child after all.

Favouritism. It’s the war cry in sibling arguments and an accusation commonly hurled at parents from their teenage children: You’re playing favourites.

The standard response – “I don’t have a favourite” – is almost a reflex.

But now research, damning research, has shown the hysterics from siblings (particularly older siblings) might be somewhat justified.

Yep, Mumsnet, described as the “UK’s biggest network for parents”, has surveyed its 12 million monthly visitors and found that, yes, parents and grandparents, too, definitely do have “favourites”.

The survey, conducted in May 2016 with 1,185 parent respondents, found nearly a quarter of Mumsnet users with more than one child admitted to having a favourite child.

More than half (56 per cent) of these parents said it was their youngest child they preferred. Mostly, they listed “easiness” as the reason why, as opposed to the “trickiness” and “demanding” needs of other siblings.

More touchingly, 41 per cent of those parents with a favourite child said the child reminded them of themselves as a youngster.

But, as parents everywhere will understand, having a favourite isn't without burden. Half of parents said they felt "awful" for having a favourite, and 78 per cent said they think it's damaging for the other siblings.

LISTEN: What to do if Grandma won't stop feeding the kids unhealthy food. Post continues after audio.

Then, there are the grandparents, surveyed through sister site Gransnet, who confirmed what all children have always known to be true: They have favourites, too.

All up, 42 per cent of Gransnet respondents admitted to having a favourite grandchild. And this is where older siblings win some ground back.

Grandparents are less likely to care if the child is "easy", the survey found, and are more likely to favour their first grandchild (39 per cent).

The way the child makes them laugh contributes to their favouritism, and one-third of grandparents with a favourite said the child reminds them of their own son or daughter.

It's one of those instances in which data proves something we all know to be true.

And while the "I don't have favourites" myth might be busted, at least many, many parents are feeling the same way.

LISTEN to the latest episode of Mamamia's podcast for imperfect parents, This Glorious Mess: