RE: My 7 year old's first deer- we can't find it???
Sometimes a deer will go in one direction and all of the sudden they will backtrack the same trail they came up. That almost happened to me. i shot a doe and she was going one direction and all of the sudden she changed direction on a dime. There might be a good chance that the deer is not that much farther from the place you saw that pool of blood.
Another thing I would suggest is to use a heavier caliber like a .243 next time. Im sure your 7 year old can handle the recoil. Anyways good luck finding that buck.