First, I will give you a bit of advice. Doing practicing questions does not equal practicing medicine. You really can't study or read on how to diagnose a medical complaint and practice test questions are really designed to examine your ability to take a test and have actually very little relevance to real medicine. I only say this because before you go and spend money and time on doing practice questions for residency, you'll realize within the first week of residency that what you read about how to be a doctor in medical school and what it is like to actually be a doctor are very different. I would suggest taking that money and time and going to Hawai'i before residency, that would be a better use in my opinion (even though I know you didn't ask for it 😀). Also, residency is suppose to teach you what you need to know to practice medicine and should give you most (but not all) the knowledge you need to pass the pediatric boards.
That being said, I didn't use Medstudy. I think most people use PREP (which residencies give you for free), 1 review book (First Aid or Laughing Your Way) and +/- Zitelli's. I think Nelson's or Rudolph's (either, not both) is also a good investment.
