The advice we are usually given as D.O. students is to refrain from taking the USMLE unless you are quite sure you are going to pass the exam. Without the exam, allopathic programs will compare our COMLEX scores with past resident's COMLEX scores in order to gauge our future success (as a test taker). If, however, you do decide to take the USMLE and do poorly, then you have now placed yourself in a position to be compared to all others that take the USMLE and do well.
Now, does this mean that you will not get an allopathic residency in pediatrics? Not necessarily. As with all failed exams, retaking it is probably the best course of action at this point, especially if you're applying to top end programs. I do not know what your COMLEX score is, but there is a difference between "passing" and "acceptable." As a D.O. student, I decided to not take the USMLE (for monetary reasons, and not competency) and applied having only taken the COMLEX. I was granted 13 interviews at allopathic programs, of which UAMS/ACH is my number one. I have been informed through my interviews that programs wish to see at least a 500 on your Step 1 and Step 2 before considering an osteopathic student for an interview. For reference, a score of 500 is considered the mean, whereas a 400 is considered passing.
I cannot say that your chances are nil, but it would be more likely for you to have better chances with a retake... IMHO, of course.
Good luck to you!