Is secularizing Christian symbols blasphemy?

2Pe 2:1 But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them, and bring upon themselves swift destruction.

Strong's Greek heresies

G139

αἵρεσις

hairesis

hah'ee-res-is

From G138; properly a choice, that is, (specifically) a party or (abstractly) disunion. (“heresy” is the Greek word itself.): - heresy [which is the Greekord itself], sect.

Tit 3:10 A man that is an heretick after the first and second admonition reject; Tit 3:11 Knowing that he that is such is subverted, and sinneth, being condemned of himself.

Strong's Greek heretic

G139

αἵρεσις

hairesis

hah'ee-res-is

From G138; properly a choice, that is, (specifically) a party or (abstractly) disunion. (“heresy” is the Greek word itself.): - heresy [which is the Greekord itself], sect.

Magical creatures would not be a heresy with any relation to the Christian faith as described in the Bible by a Bible Literalist. The creatures and beings never held any union with Christianity to disunion. A heretic according to the greek and bible context is someone who split off into a separate group and refuses to acknowledge the legitimacy of other groups or receive correction by people they should be associated with. Heresy eventually leads to denying the Lord Jesus Christ Himself but not all things which deny Christ are heresy.

Mat 13:44 Again, the kingdom of heaven is like unto treasure hid in a field; the which when a man hath found, he hideth, and for joy thereof goeth and selleth all that he hath, and buyeth that field.

2Co 6:15 And what concord hath Christ with Belial? or what part hath he that believeth with an infidel? 2Co 6:16 And what agreement hath the temple of God with idols? for ye are the temple of the living God; as God hath said, I will dwell in them, and walk in them; and I will be their God, and they shall be my people. 2Co 6:17 Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you,

Luk 11:20 But if I with the finger of God cast out devils, no doubt the kingdom of God is come upon you.

Jesus very frequently used parables to tell stories however you notice that in every parable the power of God is absent. He does not make stories up about God using his power in any other way than through His ministry and the ministry of the prophets. Always his stories are relating some common principle and doctrine of the word. Jesus never describes God's power as a magic trick nor does he relate the majesty of His excellency in any other way than reverence. He never compares the devil and the Father in some kind of tug of war. He describes the power from God which is used to cast out devils as finger power, not hand and definitely not arm as if God is barely do anything. All other stories pale in comparison to those thought of by the Master however we can judge them by some of the characteristics which the master left for us.

1Ti 1:4 Neither give heed to fables and endless genealogies, which minister questions, rather than godly edifying which is in faith: so do.

2Ti 4:4 And they shall turn away their ears from the truth, and shall be turned unto fables.

1Ti 4:7 But refuse profane and old wives' fables, and exercise thyself rather unto godliness.

Tit 1:14 Not giving heed to Jewish fables, and commandments of men, that turn from the truth.

2Pe 1:16 For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty.

G3454

μῦθος

muthos

moo'-thos

Perhaps from the same as G3453 (through the idea of tuition); a tale, that is, fiction (“myth”): - fable.

Fable is a bad Bible word but despite the fact that the word fable can cover all fiction doesn't mean that it's Bible usage includes every possible work of fiction because as I just pointed out much of Jesus's ministry was fictions which told moral stories. 1Ti 1:4 the word heed could also be translated pay attention to or be cautious about with the central idea of regard and respect. Again 4:4 of the same book shows that people have gone further into idolatry and have stopped respecting the truth in favor of their work of fiction. Verse 7 points out the error of receiving heathenish or wicked old wives tales.

Deu 12:2 Ye shall utterly destroy all the places, wherein the nations which ye shall possess served their gods, upon the high mountains, and upon the hills, and under every green tree: Deu 12:3 And ye shall overthrow their altars, and break their pillars, and burn their groves with fire; and ye shall hew down the graven images of their gods, and destroy the names of them out of that place.

Children need to be taught to respect the word and to disrespect all other things which are not the word. The primary way you do this is by spending time with them in the word and prayer. Taking them to church where they have a fun time while learning God's word. Children have difficulty telling the difference between reality and fantasy and they need to be taught that certain commonly believed things are in fact imaginary. The Bible might call this destroying the altar or hewing down the graven image.

1Co 13:11 When I was a child, I spake as a child, I understood as a child, I thought as a child: but when I became a man, I put away childish things.

Jas 4:17 Therefore to him that knoweth to do good, and doeth it not, to him it is sin.

If you taught your children: This is just imaginary there is real supernatural power but it is not anything like this. There is no santa claus ect ect. We devote our life to believing in Jesus but Jesus does not need us to believe in Him. Abraham probably worshiped the moon before he met God like Abraham we don't worship the moon. Its just a rock. God does not tug of war with the devil its easy for Him. I'm certain you can show your children the movie and it would not be blaspheme. However if you have a doubt "this might be sin", "they might turn from Christ as a result of seeing it" or the like you should refrain. You can find an in detail synopsis of the movie at the movie spoiler here.