There seem to be theological errors in this church’s take, but as your son probably doesn’t grok Christian theology anyhow, it would be meaningless to say he sees errors in this particular Baptist church’s version of theology.
Evangelicals teach that hailing Mary is wrong, that it is something God never wanted, but this is not classified as an unforgivable sin.
MATTHEW 12: 31-32
“Therefore I say to you, any sin and blasphemy shall be forgiven men, but blasphemy against the Spirit shall not be forgiven. And whoever shall speak a word against the Son of Man, it shall be forgiven him; but whoever shall speak against the Holy Spirit, it shall not be forgiven him, either in this age, or in the age to come”.