I liked it. I think it actually went against sexism, in that Mrs Claus was the one with the gadgets and doing the best job :-p
I used to love the Naughty Little Sister books..... Now they depict young girls as terrors as much as boys get the press for.
But this advert wasn't about materialistic things as such (well it was as it is a clothes shop advert but....). But more the fact that the brother teases, then goes too far, and is affected (maybe proper empathy for the first time aged 6 regardless of sex?) By how upset his sister gets about her favourite shoe being destroyed. So he tries to rectify that.
They could have switched the sexes. They could have had an all boy or all girl offspring set up (2.4 families wind me up having never been in one!) But in the grand scheme of things I do think people may be reading a little too much into the advert and what younger viewers may think.
And the "reinforces idea all women should take their husbands name on marriage" - she has always been known as Mrs Claus. You can't change that to suit your own situation surely? That's like saying actually Jesus was a girl, to make it fair nowadays. (Although I will argue God is a woman sometimes!)