I'm very happy with Pediatric Healthcare associates in McKinney off Eldorado, near Hardin. My son needed an X-ray yesterday and they sent me to the Hospital off 75 and Virginia which was very close.
Here is their website - I've seen Menchaca and Dr. Frank. Both have children of their own so I feel they have real life experience to add to their job.
FYI - their nurse line is AWESOME and they always get back to me promptly when I have questions on whether I should bring my children in or it's not a big deal about something that have.
http://www.phamckinney.com/web265/
They came highly recommended from some mom's in my mom's group when I moved to Texas and we've been using them for almost 2 years now and I'm super happy. I never have issues making appointments and the staff is super friendly.
Good luck!!