catapres, how much is an overdose | ADHD Information

My 7 year old son is on Ritalin and Catapres for ADHD, one catapres tablet in the evenings. But he has returned home early from a vacation.  On unpacking his bag I carelesly left his meds on the kitchen bench there was three doses left.  I have no idea why but instead of taking one tablet he has taken three.  It is the middle of the night here in Australia and was just wondering if I should be really really concerned or just keep an eye on him.  he has never done anything like this before we usally have to force him to take one.  worried