Try to notice as many good things your children do as possible!!!

As soon as possible after your child does something good comment on that thing (be specific as to what the good thing was), and give your child praise for having done that good thing. Example - Your young daughter falls, hurts her knee, and begins crying. Your son seeing this goes over to his little sister, helps her get back up, and comforts her. Having observed all this take place you go up to your son right away and say something like,

"I saw you help you sister get up after she fell and then tried to make her feel better. That was really nice of you to do. I feel good to have a son who loves his sister so much."

Also say to your son,

"Allah Subhanahu wa Ta'ala will be very pleased with you for helping your sister."

Things to remember...

1. Give the praise as soon as possible after the good deed.
2. Say specifically what the good deed was.
3. Give the praise sincerely and in a loving manner.
4. Have variety in how you give praise, don't always say the same thing.

NOTE – Notice how in the above example the praise given had three parts. First the mother told her son what he did was a nice thing to do, second she told him how it made her feel good, and third she took the opportunity to let him realize how much he loves his little sister.