Parents talking and explaining issues to children of any age (even babies) is very important. Talking to a child who kicks their legs and reaches for the spoon with yoghurt on it "Hmmm, you are enjoying your yoghurt today. You like strawberrries". or "Oh, that's different. You don't know what to think of that taste, do you?" to an infant who has been given pureed pumpkin for the first time and has grimaced. Saying to a young child as you pass him/her to grandma "Grandma wants to cuddle you now. She loves you so much."  Children may not not understand all of the words but they do pick up on the voice and facial expressions, and that is one of the ways they learn. Only yesterday, I heard a young mother talking to her 2 year old. The child screamed when the mother took her car keys off her. The mother responded--very quietly and gently--"We don't shout at each other, we talk nicely. I can't let you play with the car keys , but you can play with ..." 

Talking to children does work, and it develops their ability to listen and understand. 

It is not unusual for siblings to fight (for whatever reason ), and some parents might even say it is not unusual for siblings to physically hurt each other. However, your older child is presumably bigger and stronger than your younger child and, as you have seen in this instance, can hurt your physically considerably. Even children of the same age and size can really hurt one aother if they use unacceptable means to solve their problems. 

Bring the two children together. Tell them that every one has a right to be safe at all times. Set simple rules such as 1. Only use kind words 2. Use words not actions 3. Keep your hands and feet to yourself . Write these rules up and put them where the girls can see easily see them. You might like to stick a picture or photograph (or even a drawing) to illustrate the behaviour that you want. Of course, you will write these words in your own way. Just make them brief and positive (eg use kind words rather than don't swear).

When a child breaks one of these rules, and that will happen. Quietly and definitively say to the child. I cannot allow you to --speak to x in this way/ hurt x in this way. Remember our rules or have you forgotten our rules?  Let's see what they say. Read the relevant rule to/with the child pointing to each word and the picture. If the child starts to say, she did this to me first or something of that nature, tell her that you will speak to the sister in a moment, but you are talking to her about what she has done first. The important part is to deal with the child in a calm and no-accusatory way. Suggest what she could do next time something like this arises. 

Finally, taking the time to help your children learn the social skills they need to play happily together is rewarding. You might think a four and a two year old are too young to talk to in this way. I can assure you that you will be  pleasantly surprised. Add a little bit of adult modelling and . . .

Hugs Tee