There are a ton of different classes of ADHD medications that are all very different. The most popular- stimulants like adderall and ritalin are probably the most well studied psychiatric drugs in history, and not without some risk of adverse effects, but overall are quite safe even for young kids.
Untreated ADHD itself is far more dangerous than any of the medications: high rates of mortality, suicide, addiction, job loss, relationship difficulties, car accidents, etc.
There is also some evidence that giving children stimulant medications for ADHD can make it less likely that they will continue to have ADHD as adults.
The non-stimulant ADHD drugs actually all have worse side effects than the stimulant ones, and they're harder to stop taking. You can quit Vyvanse cold turkey or take it as needed and be pretty OK, but if you quit Strattera it takes weeks to work again once you start it.
And you can't quit Intuniv without titrating off for a week or two or you'll feel pretty sick.
Untreated ADHD itself is far more dangerous than any of the medications: high rates of mortality, suicide, addiction, job loss, relationship difficulties, car accidents, etc.
There is also some evidence that giving children stimulant medications for ADHD can make it less likely that they will continue to have ADHD as adults.