Would like to install a pulley in tree house for grandchildren using pulley, rope and bucket. Not sure how to do it to make it safe. Any help?

I suggest:
1) making sure the bucket is too small for a child to try to "ride" in.
2) locate it where it would be impossible for a child to climb into the bucket when it's at the "up" position.
3) let the "weakest link" (such as the bucket handle) be too weak to lift a child off the ground. For example, if the handle of the bucket was plastic and kids tried to lift one another from the ground in the bucket, the handle would break first.
4) locate it where a child in the treehouse doesn't have to lean out over open space to reach into the bucket.