Is it good for kids with adhd to take a ritalin (methylphenidate) breaks?

Depends: Research has been mixed. In the 80s, standard practice was just school days. In the 90s & 00s, with once-a-day versions, standard moved to daily use. What's nice about stimulants is, they work only on days you take them. If your child shows clear benefit & no se with daily use, great; if appetite and height are of concern & weekends not a problem, skipping or using a lower dose may work well.

No: Adhd doesn't take breaks, so it's treatment shouldn't either. Would you take breaks from Insulin in your diabetic child? Getting to correct dose of stimulant takes time. Stopping it for periods of time exposes the child to restart side effects. More importantly, the adhd isn't treated & the child could regress, get into trouble, or if older, start using tobacco alcohol or marijuana while off.