[BipolarBob]

If Mary had other children, then why did Christ create a new son for her on the cross?

He didn't.

Christ was Mary’s only child.

An non proveable and contrary to evidence statement.

[imardmd1]

"When Jesus therefore saw his mother, and the disciple
standing by, whom he loved, he saith unto his mother, Woman,
behold thy son! Then saith he to the disciple, Behold thy
mother! And from that hour that disciple took her unto his
own home" (Jn. 19:26,27 AV).

Virtual son, virtual mother. We don't know all the reasons why, and it would be
impertinent and presumptuous to innovate a doctrine from this passage.