Preschool Problems

So my son who is 4.5 years old started pre-school last week,with his brother being born and going to special care to see him twice a day I think he has been out of sorts,but mostly acting like himself.Normally he is a kind,compassionate kid that stands up for himself but never hurts anyone,speaking to the teacher(who didn't offer the info I had to ask),he has befriended a couple of kids that aren't a good influence on him and he is not sharing and hitting other kids.
This is the first time he has been away from me,I am wondering if it's a phase and he will settle down or should I be concerned?He is also quiet an intelligent kid who can read and write (basic) and knows basic math,I have spent years teaching him to prepare him for school and I don't want him to regress.Any suggestions?Sorry for the length BTW

Gosh, I don't know what to suggest. Have you spoken to the teacher in length about your concerns?

It sounds to me like he may be acting up because of a new sibling...but then could be the kids he has befriended.

i have a 5 yr old son whos been in school since he was 3 yrs old...i wouldnt worry i have been thru this with my son as he is 2nd youngest of 5 children he had to learn to fight his own battles and took that into school sumtimes picking on other children...i know it sounds cruel they soon learn that unlike if mummy was there to protect them in school there are other children that will hit them back and take toys off them...its just a passing phase he will grow out of it given a bit more time with the other children...also one minute he will be friends with the other little lads the next minute they wont be...u know how children are...

its prob a bit of jealousy too...hes still only a baby himself

children are like adults they learn from experiences of life

good luck