No I most certainly would not treat my DS and DD alike! Quite simply because one is three years older than the other and they are very different people with different personalities , likes/dislikes and needs.
I doubt that other parents here would not agree!
What I think you may be asking here is to do with perceived fairness and equality? Perceived on both sides.
Now a child judges such interactions at a moment in time; in the context of a current interaction. They are also likely to choose their own 'spin' on the issue! As a longterm parent your perspective - detailed or not so detailed memories - will be more accurate yes; but that is not really the issue is it?
Many parents do find that they like/love/prefer one child over another. This is inevitable as children are a genetic lottery. To take an extreme example no-one is to blame if your child is a psychopath who tortures animals and is clearly likely to offend seriously - this is in fact a desperate actual situation for some parents. So, though most cases will not be this extreme, they pose questions as to how we choose to respond consciously.
My sister and her husband cannot get up in the morning - in fact they are horrible and cross - but one of their children is an early bird. He saw them at their worst and they actually locked him out of their bedroom when he was six. When he came to stay with us we were all four early birds and morning was a joyous fun time with chocolate and croissants in bed and chatting. He was 9 by then and we talked about how his experience of strife and unpleasantness was not parental choice but a 'conflict of natures'! Not surprisingly young children do not see things from their parents' point of view but in relation to themselves.
But there are in infinite variety of combinations so there are unlikely to be simple answers so beloved of the agony aunt! What we can do when we notice these things or they are brought to our attention by an angry child it to listen (first and always), observe, analyse, share and discuss to gain insight; apologise, accept and work out a way to cope. Above all don't play the blame game - that is not meaningful or helpful. This is perhaps one of the hardest tasks facing a parent - and one that all the books seem to avoid as if mentioning it would be too harsh...
Please don't think that we do not have our issues - we were lucky that our two are wired so like their parents and that suits us. But similarity leads to conflict as well as mind-reading...
I asked my son's best friend who lives here (having been thrown out by his parents for abandoning his A Levels) what his perception was. He observed that we were very fair albeit the youngest by three years did get the best deal! He then told me a sad tale of how his mother had openly treated her boys very differently; he was not approved of. I hope giving him space to explore this has helped him process these experiences and recognise them for what they were.
Best wishes to you all - get stuck in but do not beat yourselves up! After all tomorrow is another day...