Christians disagree about what idolatry is. Catholicism and Eastern Orthodoxy see Christian art and icons as good, because they see Christ's Incarnation as having made images of God lawful. However many Protestants regard much Catholic art as idolatry.
This is due to differences in the understanding of the Ten Commandments. "You shall have no other gods before me. You shall not make for yourself a graven image, or any likeness of anything that is in heaven above, or that is in the earth beneath, or that is in the water under the earth; you shall not bow down to them or serve them; for I the Lord your God am a jealous God, visiting the iniquity of the fathers upon the children to the third and the fourth generation of those who hate me, but showing steadfast love to thousands of those who love me and keep my commandments." (RSV Exodus 20:3-6)
Idol Facts for Kids. Kiddle Encyclopedia.