biting 9 week old rat

Question
QUESTION: We have a 9 -10 week old male rat that up until the past week has been fine. we got him with his brother, and he has become quite protective of him and every time we put our hand in the cage he bites. he also will sleep outside the hide away door while his brother sleeps inside.this is a new pet for me as i'm used to the typical pets (ie dogs,cats,etc...) not sure as to why this has suddenly occurred?any info would be greatly appreciated as i have 4 children that handle them both all the time.they are not mean to them like i have seen other children be to small animals.

ANSWER: Does he only do this inside the cage, or is he doing this outside the cage as well?

I'm sorry to answer a question with a question, but if you can specify, I may be able to help you more.

---------- FOLLOW-UP ----------

QUESTION: Could the fact that he only does this when he will be left alone have anything to do with it. that's why i think its jealousy.
also completely off subject i have been giving them the Kaytee Fiesta max since we got them with other things such as  Cheerios, Broccoli,apples, grapes,baked turkey and hard boiled eggs just to name a few things. should they also receive a salt lick(that's what my husband called it)or something with salt,they do a lot of licking?

Answer
That actually could have a lot to do with it - he may be upset thinking something 'got' his brother, being very attached to him, or fear when he's alone. He may outgrow this eventually.

They don't really need the extra salt, unless you notice they're not drinking enough during the winter or it's been extraordinarily warm and they're not drinking. The sodium isn't the best thing for them. The rest of the diet sounds perfect, though!