While the Virus was not fully sentient it had some intelligence. The reason for the focus on children was quite simple.Adjusting children was easy. Teenagers harder. Adults almost impossible.
Still mistakes happened sometimes. Such as infecting someone who was only a child due to a previous infection.
The Virus looked over the sphinx, finding all the problems it had created for her.
Problem one, her girlfriend was no longer interested in the sphinx.
Second problem, she was attracted to a guy who has a female friend already.
The Virus looked into it's database to try and find a solution. The lion pride would allow all four to be together. But their is only one king and one queen. Only one relation is romantic so one of the sphinx and the girlfriend must be the king, the sphinx already changed so the girlfriend must be the king.
Now out of the three remaining, two have already been changed. The non-changed one also a relation with both of them already.
The virus having made the decision about the roles now looked for the perfect forms.
Anthro forms are the most useful in general, but the taur form has lots of advantages for the Queen in terms of raising the cubs.
Decision made the Virus started the change in Sarah and Jon.