I just finished reading The Adventures of Tom Sawyer again. Lots of fun! Great adventure and drama, characterization, and historical period interest. Hilariously and well written. Mark Twain did an amazing job of presenting these adventures exclusively from the perspective of a young boy, while at the same time making some decidedly insightful observations about human nature (adults in particular).
Is this a good book to include in the reading list for your children? Yes! However, there are certainly some murderous and gruesome aspects. It may not meet your standards for younger children. My strategy is to carefully allow my children to experience real life and help them understand it from a biblical worldview.
Another important thing to be aware of is that Tom and Huck are not operating from a biblical worldview. And their view of those that seem to be is less than flattering. There is a certain morality in the story as the boys become heroes for choosing to tell the hard truth, at their own peril, for the benefit of others! However, the book also ends with their certain intent to become "robbers". The boys are at the time of life when playtime and reality are blurred. This might be difficult for young readers to process.
It is worth reading. It is worth letting your children read, if you are prepared to help them process it. But that should be normal life, anyway.