7 yr old grandson has been In karate about 4 classes now. He used what he learned on my 3 yr granddaughter.I think he needs to learn when to use what he learns. His mother lets him get away with murder bc she feels sorry for him bc his real father has been absent since he was 3. My granddaughter needs to learn to protect herself from her bully brother. Is 3 yr old too young to learn self defense?? She is very smart compared to most her age.
As Ian MacDonald said in the comments, your grandson should be disciplined. He needs to understand that hitting people is wrong (except in self defence).
Having your granddaughter learn some karate is not the answer for the following reasons:
She is physically weaker and less coordinated than your grandson. There is no realistic prospect of her being able to fight your grandson off.
Teaching her self defence as a remedy is sending the message that if she cannot fight him off then it is her fault for not being better at fighting than he is, so it is really a subtle form of victim-blaming.
Your grandson will get the same message; its OK to hit her because its her fault she is too weak to fight him off.
Children need protection from the dangers of the world around them. That is the responsibility of the adults, not the children.
Bullying is child abuse; if someone punches you then it hurts just as much, regardless of how old the fist was. If an adult hit your granddaughter I am sure you would immediately phone the police. It shouldn't be tolerated just because the abuser is also a child.
That isn't to suggest that children should not learn how to defend themselves, but it must be in a context where it is the last line of defence after the adults have failed, not the first and only line.