Tariq Lane couldn't persuade Kallie, knowing that she was cruel and ruthless, not caring about the child's life or death, and only wanting to replace the child with Edward Anderson's baby.
In the end, Tariq sent Bella Scott into the delivery room, and Kallie was giving birth in the next room, with doctors arranged by Tariq in both rooms. Kallie didn't trust them, so she sent people to watch their actions.
If he didn't switch the babies, Kallie would know that something was wrong.
But Tariq had his own plan: the children were to be switched, but he brought Kaelin Anderson's illegitimate child over and waited for Bella to give birth, then let Kallie raise Kaelin's child.
As for Bella's son, he would take him with him for the time being and make a decision based on future developments.
And Bella's beloved daughter, he didn't plan to touch. From Bella's words, he could tell that she seemed to be particularly fond of this daughter.