First and foremost, discipline is not equal to punishment. The key point of discipline is not to punish the kids, but to teach them the correct ways of behaving: understanding the rules and boundaries, acting with kindness and consideration.
At their ages, children's mental capability is still developing, it is very wrong for you to expect your children to put themselves in other's shoes and punish them for failing to do so. It is in fact better for parents to put themselves in their children's shoes. It will help you to avoid losing your temper.
Discipline is also not about saying 'no' or 'yes' without any further explanation. In many situations, children behave 'badly' just because they are trying to figure out what is the right way to behave. Mere punishment or shouting 'no' does not help them to figure out what is right or wrong.
Instead, discipline should be about parents demonstrating the right way of behaving or explaining what is right or wrong. When a child makes a mistake for the first time, it is important for you to act as a coach, but not punisher. You should explain to him or her why it is wrong to behave in that way and what should be the right way to behave. Parents should also allow the children to explain themselves and let them ask questions during the coaching. Sometimes, due to their mental capability, they may not be able to understand the big reason behind your coaching, but that is fine, if you explain to them nicely, they will listen.
Lastly, if your child does behave badly in certain situation after you have explained to him or her the right way of behaving in that situation, it will be good for you to give them some sort of light punishment.