I have namechanged as this might make me identifiable.
I have a sister who is 2 years younger than me. She has always been my parents' favourite, although of course they vehemently deny this. As children, I would always get the blame for things even though my sister often behaved in a sneaky manner to get me into trouble. I was always labelled as the difficult and unpleasant child, even though I was just a normal child, and my sister was the little ray of sunshine.
When I had my first child, who is now 10, my mum made it very clear to me that she would not be doing any babysitting, 1) because she didn't agree with mothers going to work and that they should be at home with their babies and 2) because she didn't agree with parents having nights out. She also was adamant that DH, DC and I needed to be a family and to be left alone, therefore she didn't and wouldn't help at all in the early days, even when I was crippled with PND. Of course, I didn't expect any help even though it would have been nice, and certainly wasn't expecting her to provide childcare whilst I worked. Over the years she has always refused to help me out, even if I've been ill and just needed her to have my DCs for an hour or two. She is always busy, or says that we need to be a family. On the rare occasion that she has babysat in the evening she has insisted that I pay for it.
My sister had her first child 5 years ago. Straight away my mum was different with her. She stayed at my sister's house for a week, doing all of her housework and getting up in the night with my DNiece. My sister's parents in-law are very hands on and very doting grandparents, so immediately my parents were in competition with them. My sister went back to work full time when my niece was one, and my parents immediately started doing 2 and a half days per week of childcare, for free, whilst my sister's in-laws provide the other 2 and a half days. I said to my mum at the time that I thought she didn't agree with working mums, and she said that it was different with my sister as she has a degree and I don't!
My sister and I have each since had another baby, and my parents barely see my children, whilst showering childcare and presents at my sister and her children. I know material things shouldn't matter, but it is hurtful. My parents are also still providing free childcare, and having my sister's children all weekend sometimes, so my sister and her DH can go on weekend breaks. They have never once had my children overnight!
It is getting to the stage now where my children are picking up on it and saying that Nanny prefers DNiece and DNephew to them, and it is hurtful for them for example at Christmas when they get so much less than my niece and nephew and they have all opened their presents together.
I have tried to calmly talk to my mum about it but she is certain that she treats them the same and dismisses it as me being jealous or nasty. 
AIBU to think my parents are unfair?