Millstone Water Feature What And Or Who "shall Offend One Of These Little Ones"?

What and or who "shall offend one of these little ones"? - millstone water feature

... Whoever believes in Jesus Christ.

Mark 9:40-42
Because he is not against us is on our side.

For whoever gives you a cup of water to drink in my name, because ye belong to Christ, verily I say unto you, that does not lose his reward.

And who introduces these little ones who believe in me, it's better for him that millstone around their necks and were thrown overboard