Zyrtec has helped my one year old's eczema. My eldest who is now 6 has taken it for a year now. I have seen some possible mild behavior responses. Now that he doesn't need it as much we are testing this possibility. I would suggest looking into which type of zyrtec a child is taking. You may want to question the use of aspartame sweetner as a possible culprit in causing issues with behavior and stomach issues.