I would say that if you can kneel, kneel, as long as you are not in someone’s way or creating a hazard for them.
But please don’t judge the ones who can’t kneel on a hard floor. Thank you for being kind.
We do a special Family Mass at our parish. It’s in the school gym, and usually pretty packed, with people up in the bleachers. No one kneels. The floor is hard and dirty (it’s a gym floor, after all), there’s no room to kneel safely in the bleachers, AND many families are tending several tots, and they have to be able to give chase when the little ones charge up towards the altar!
There is another Mass going on at the same time in the sanctuary, and those who want to kneel (on comfortable kneelers) are free to attend that Mass. No one forces families with small children to attend the Family Mass, so many families take their little ones to regular Mass. But for those families who wish to attend a little more “family-friendly” Mass–nothing different about it, but almost everyone there has babies and small children, so you don’t feel self-conscious about your children’s little noises–it’s nice to have the option of Family Mass.
There is one difference between Family Mass and regular Mass–the priest calls all the children to the front–they sit on a huge rug in front of the Altar–NOT up in the “sanctuary” (It’s a make-shift sanctuary, but it’s a sanctuary none-the-less). And the priest does a homily just for the children, and after Mass, they always get some kind of take home surprise related to the homily.