Many children develop imaginary friends during their early childhood years. This can be seen as an indication of your child's developing imagination.
Young children often appear to lack empathy although as human beings, it is natural for us to be aware of other people's feelings and showing concern towards them. This is a very important trait that we must all acquire.
If you have two children with a small age difference, it is very common to find arguments and jealousy between them. Most parents refer to this as sibling rivalry.