One of our female kittens is showing all the signs of being in heat. She's one of two - the rescue thought they were about 9/10 weeks when we got them, but the vet thought one of them was about 8 weeks and the other might be a bit older. If the vet is right, the older one is about 12 weeks. Is it normal for them to reach maturity this soon? And is there anything we should do beyond the normal? Obviously we will get them both spayed as soon as they're big enough, and we're keeping them in.