What does it say on the side of the bottle? Usually there's a guideline.
There is a clear one for one year olds. If younger ask your pediatrician. I didn't give my son anything other than formula/breastmilk until 6 months. He was close to a year old the first time I gave him pedialyte .
I had to give mine pedialite around 7 months I think it was. Then again at 10. First time was a tummy bug. Second time hand foot mouth.