Of course it's basically due to the born character, but there must be some way to train/improve them.
I heard my friend said she knows some 冇耐性同心散 children being better after learning 日本劍道. This sport requires high level of patience and consentration.
I think the method/attitude that we deal with our children can also train/improve them.
I agree with lilac that you can 睇多d有關書籍及聽d講座. 3yrs old is still young but you should start training your children as soon as possible. It's more and more difficult to change our children when they're getting older.