I did Paws Across Texas for several years with my golden, she was a rescue so don't really know her age but guessing about 5. We were not perfect but very calm so they let us in. We still had lots to learn but loved the experience.
Several years later my girl had died, I had rescued a Dalmatian... possibly lab mix. He was actually better with people than the golden and absolutely LOVED kids. My golden would get up and move when she had enough. The Dal would roll over and ask for tummy rubs, he was wonderful and what kid doesn't love Dalmatians. This was when the 101 Dalmatians came out and even the youngest kids knew what a Dal was.
Well we went back to Paws and all the ladies on the board of exams loved him. He was quiet, gentle & obedient. There was a lady there with a dog that whined through the entire thing, poor dog was so anxious. But the lady had been with the group for many years with another dog so she passed, even though the dog didn't do anything correct in the obedience portion. Turns out the lady that runs the group didn't like Dalmatians. Seems they had one in the group previously and it didn't go well and guess all she saw was a insurance claim waiting to happen. Everyone but the leader voted us in but it was an uphill battle from there. Because the leader of the group disliked Dal's so much we were not allowed to do any locations with children. Seeing kids was his strong point! I had volunteered to do the Special Needs event as my grand children were going to compete. I called this lady several times to confirm our participation and the day before the event she said we could not go and would not be allowed around kids for 3 yrs., we were on probation. She really didn't want us in the group and after all, it was her group. Well I was heartbroken and resigned from the group.
So I went on my own to Ronald McDonald House, The Warm Place (place for abused kids) and the Fort Worth ISD let us do the special needs classes. Just had to meet with someone in charge, provide all vet records and a recommendation from the vet as to temperament.
We also went to day cares to give classes on how to treat your pets and show kids how to teach their pets to sit & down. Not being part of the group kept us out of the children's hospital but that was ok, I didn't really want to work with this lady anyway.
You just never know how some of these groups work. Don't take it personally, just keep working at it and give your guy time to mellow. Might see if there is another therapy group in the area. Here is a pic of my Dal that she felt was unsafe around kids.