I have been with DH since DS was about 18 months old. He has just turned 6 and we have a DD of our own who is nearly 3.
MIL treats them completely differently. I understand that she can't possibly love DS like her own bio grandchild, but she is really blatant about it IMO. Also, he has been part of the family since he was a baby so you would think there would be some kind of bond there. Apparently not.
Every birthday and Christmas DD is showered with gifts, usually at least £100 quids worth. Don't get me wrong, its lovely that she loves DD so much and gets her nice things, and, to be fair, she does always buy for DS at these times too.... but its always something cheap and thoughtless. In fact, last Christmas she told DH to buy DS something from her and wrap it up etc for about £10 and she would "refund him"
she couldn't even be arsed to think of something for him. Also, she regularly asks to babysit for DD and DD has her own room at MIL's. but she would never entertain babysitting DS as well.
When we visit, or she comes here, she practically ignores DS and he can sense it i think because he usually acts up and its like he is trying to draw attention to himself :(
Anyway, she really surpassed herself this time. It was DS's birthday at the weekend and DS received (through the post) from MIL, a cheap card with £5 in it. I was so pissed off but didn;t want to say anything to DH as he thinks the sun shines out of her arse and he gets really pissed off if I dare say anything about her.
(Ironically, DS's grandma (my exMIL) adores both DC, even though I have been split with DS dad since he was a few months old, and says she classes them as her grandchildren. She has become a good friend and she even invites just me and DD round for lunch etc when DS is at school. My DD even calls her Nanna. )