Our son has done fabulous on Concerta. No side effects right now, other than a decrease in appetite at the beginning (which you can make up for with breakfast and dinner). Our son did see his tics get bad on Concerta when we had to boost the dosage to the max, but we've since lowered the dosage and he's fine. I can't say enough good things about what Concerta has done. Completely transformed everything. People don't even know he has ADHD when it's active. The only downside is that it doesn't last all day, so we're still dealing with severe ADHD-combined type later in the day.
We first started off with Clonidine and Tenex (now marketed as Intuniv) which are blood pressure meds. They did zip for our son's ADHD, but are known for mild side effects. Then, we tried Ritalin. WOW! Day one, huge transformation. We got to see our real son. Same kid, full of energy and personality, but with normal behavior. It was amazing. (Concerta is long-acting Ritalin, BTW)
After our son had the tic issue, we tried Adderall and Vyvanse, which were nightmare meds for our son. Severe aggression and rages as they wore off. Definitely not a good match for him. We went back to the lower dosage of Concerta and all has been great since.
I know how scary it is to start meds, but keep in mind that with stimulants, they're out of your child's system by the end of the day. So, if you hate a med for any reason on day one, you can stop it immediately and try something else the next day. You're in control.
Everyone I know personally with a child with ADHD has been thrilled with the benefits of medication. It really can be life-changing. Just be prepared for some trial and error to find just the right medication.
As far as telling a child about ADHD, we told our son in kindergarten. We talked to him about whether he feels like he has extra energy and it's hard to focus on things sometimes. When he said yes, we explained he has a medical condition called ADHD and it's nothing scary. It just means he has more energy than some other kids and it's why he gets into trouble a lot. We then talked about how other kids have issues, too. Some kids don't see well and need glasses. Some kids have trouble walking and need a wheelchair. Then we mentioned we're helping him with his ADHD by special medicines that will make it easier to focus in class. We then talked about how he feels when after taking the medication and his response was "much better." (ETA: There's a great book called "Cory Stories" that talks to kids your son's age about what it's like to have ADHD. Really well done. Also talks about medication.)
I wish you the best of luck as you start this journey!