Either you do both ,or you do neither.
I agree with this - and probably steer towards neither, for all of the reasons given in this thread. It's unfair to assume that all children will have a living/present/loving mother, and that it's just a nice little gesture for them, but then to slap it down as pointless and a waste of time for those kids who have a living/present/loving father.
As for the religious origin argument, how often do schools have children not only exclusively referring to it as 'Mothering Sunday' (and never 'Mothers' Day' - and then get them to make a card addressed to their mother church, to pin up on the church notice board or pop into a dedicated box there?
When you finish laughing, you might want to educate yourself and loose that dated and sexist attitude.
And it's 'lose'
The 'sexist' argument has already been covered and debated, but 'loose' is not necessarily incorrect here, depending on what the poster was intending to convey.
"You might want to lose that attitude" suggests casually allowing whatever alleged attitude to disappear, although is frequently colloquially used to suggest actively seeking to get rid of it.
"You might want to loose that attitude" is somewhat old fashioned English, but it has the clear (and grammatically correct) implication of deliberately and actively casting off the attitude in question, without any ambiguity as to intent or other ambivalence.