female kitten trying to nurse from male brother

Hi all,

We have two 12 week old kittens. We took them home 4 weeks ago from my brother's house. Therefore, we know the Queen.

In the last day or so, the female has been trying to nurse off the male (her brother). The boy does not seem at all bothered by this, but we are wondering if this is normal behavior.

Thanks

I do think this behavior is common.