I am so glad that you are thinking in terms of ear protection for your littlest fella, but I would like to encourage you to be prepared to protect your entire family's ears...especially BOTH kids!
Prolonged noise at the decibel level of most concerts is more than enough to cause permanent hearing loss. This type of loss is caused by the shearing of tiny hair in the inner ear that transmit the high frequency sounds. Each time we lose more of those high frequency sounds, our ability to hear becomes more distorted.
Like most folks, my brothers and I pooh-poohed the hearing risks in exchange for going to concerts when we were in our late teens and early 20's...now all four of us have hearing losses great enough to merit hearing aides!!
I cannot imagine what our losses might have been like had we started attending concerts at 8 years old!
I teach Deaf and Hard of Hearing kids and I know how precious hearing is...PLEASE protect your entire family if this concert is as loud as most. Each time we are exposed to this level of sound (and you would be surprised at how often that can happen in today's world) we lose more hearing. It does not take many exposures before we find ourselves hearing---but not understanding what was said.
With the fourth of July around the corner, I hope that many folks are thinking as intelligently as you are and are looking into ways to protect their children's hearing!
Moldable ear protection can be found in the pharmacy section of most stores...If inserted correctly, most of these "ear plugs" will lower the decibel level about 30dB.
You might also call an audiologist and ask for suggestions. Most would be more than happy to help you avoid noise induced hearing loss!!
Try to avoid sitting directly in front of any speakers, have your entire family wear ear protection and ENJOY the concert!!