How soon can she come in heat?

I have 3 kittens that will be 5 months old next week. There are two
males and one female. We keep them in their own room and then let
them have take over the rest of the house in evening when we are
home.

Tonight we noticed one of the male kittens being a little aggressive
toward the female and actually saw him try to mount her a couple of
times. A little later we saw the other male doing it too, but not in
such an agressive manner.

We were planning on spay/neuter when they were 6 months old, but
I'm certainly concerned by their behavior tonight. Is it possible the
female could be coming into heat?

Should we seperate them immediately??

If possible, I would separate the males and females or get them fixed a little early. She could definitely be coming into heat. Cats develop at different rates, just like people, but I've heard of cats as young as 4 months turning up pregnant.

I would go ahead and make the appointment. Cats are polyestrus, which means that come into heat depending on the seasons (usually late February, early March straight through till about October) so even though your cats are a tad young it is not out of the realm of possibility for them to start showing some behaviors.

I had my male cat fixed at 5 months and my female fixed at 6 months. I was "lucky" because I understand that females can get pregnant as early as 4 months. I would definately get the males neutered soon (by the way....this is a really good time to get cats fixed as there are many low cost clinics going on across the USA right now for spay day).

Katie

I would get them fixed as soon as you can and keep them separated until they get fixed. I had Lil' Jag spayed at 5 months and she had already gone into her first heat. Thank goodness our male cat was already altered.

My Freija went into her first heat at 3 1/2 months old (!!!). I had to endure a month of it while I saved up the money to get her spayed. Her sister Abbie, who had not shown signs of being in heat, apparently was as well when I got the two of them into the vets just before their 5th month anniversary. She apparently had silent heats. Lion and Bear became sexually mature when they were 5 months old - a month earlier than I had planned on having them neutered - but they went in as soon as I could get an appointment 2 days later.

Kathryn