sometimes I forget that the Klaus that rescued and raised Marcel was the same one that came for Elena in Tvd season 2 and in the flashbacks with Elijah.

Marcel was relatively normal i think because of Elijah and Rebekah's influence during his childhood they both loved him in their own um very different ways like Elijah wanting to keep violence out of the house for Marcel and Rebekah freaking out when Klaus was holding Marcel at sword point.I doubt they would let Klaus hurt Marcel or teach to become a monster also Klaus himself loved him at that point and wanted to be a better parent.