Country Singer John Rich -- I'm PISSED at Marvel ... Live Show Scared My Kids

John Rich is PISSED at Marvel ... he says their live show for children is anything but kid friendly -- and it ruined what should have been a great day for his family.

Rich says his 3 and 4 year old sons had been looking forward to "Marvel Universe LIVE!" for months ... but both burst into tears shortly after it started -- due to "loud explosions and aggressive audio."

The country singer tells us pyrotechnics are set off extremely close to the front row -- multiple times -- and it scared the crap out of his kids so bad he had to take them home 15 minutes into "M.U.L."

He adds, "They [Marvel] should warn people before you drop a few hundred bucks to get your kids all hyped up. Really disappointed us."

The website for the show does warn there will be loud noises and "safe" pyrotechnics.

A rep for Marvel says, "We take into consideration the ages and sensitivities of all our audiences when producing our shows, and we apologize if Mr. Rich felt the special effects were too loud."