The Lord did not create the heavens and the earth without a plan. The essence of His plan was and is to raise up children unto Himself. He created us in His image - specifically with FreeWill, the ability to choose.
So, His plan predestined us to be His children by virtue of our exercising our gift of FreeWill to receive His person, Jesus Christ, as Lord and Savior.
If we were predestined with no choice in the matter, the whole timeline of human existence makes no sense as those predestined to be His children was already fixed just as those who were predestined to damnation was already fixed.