Every parent who has thought about sharing the Mahabharata has asked this question, usually around the time their child asks why family is fighting family. The question is fair. The answers, if we're honest, are more interesting than the question itself.
What the Mahabharata is, structurally
The Mahabharata isn't a children's book that contains a war. It is a library that contains, among many other things, a war. Most of what's in the library isn't the war. Friendships. Riddles. Pilgrimages. Long conversations between teachers and students. Stories about other stories.
When we say 'the Mahabharata' to a child, we're making a choice about which shelves in that library we're visiting. The violence is on certain shelves. The shelves we visit first don't have to be those.
The parts that actually earn the worry
It helps to name them, because a specific worry is easier to manage than a vague one. Four moments do most of the work: the dice game and what follows for Draupadi, Abhimanyu surrounded and killed in the chakravyuha, Karna struck down while his chariot wheel is stuck, and the night raid at the very end. These are the pages a young child shouldn't be handed early.
And notice what makes them hard. It isn't blood. It's helplessness: a good person cornered with no way out. That's the thing a small child feels in the body, and it's why timing matters more than any amount of editing. Most of what people picture when they say 'the war' is closer to long speeches and slow grief than to anything gory.
What to say when your child asks about the war
They will ask, usually before you feel ready. You don't have to describe it. 'It's a war between two sides of one family, and almost everyone loses something' is a true and complete answer for a five-year-old. It respects the weight without opening the wound.
Save the detail for the age that can hold it. A child who already loves these characters as friends meets the war as a tragedy, which is what it is. A child who meets the war first meets only the violence, which is the thing you were worried about to begin with.
A rough map by age
Ages 3 to 6: the childhoods. Krishna and the butter, the Pandavas at school, Bhima and his appetite, the friendships. No war, and no need to mention one.
Ages 6 to 8: the tests and the smaller sorrows. Ekalavya's thumb. Abhimanyu's courage described rather than staged. The idea that good people can be caught by their own promises.
Ages 8 and up: the war, the dice game, Karna's end. By now the characters are old friends, and the hard moments land on a child who has earned them and can talk them through with you in the room.