Pay attention to the organization's definition of league age. He's 5 but he might be considered league age 6. Typically the league age is determined as of May 1 of the upcoming year as the league year runs Aug 1 to July 31.
Unless he turned 5 between May 2 and today, 6MCP is likely his league age. It's a transitional format from T-ball to CP. Batters get 3 pitches from the coach. If they don't put the ball in play they hit off the T.
I coached for 25 years and ran leagues and tournaments. Buckle up for full-time 7 and 8 CP. They were our #1 and 1A problem leagues with coaches and parents.
Great age and great memories when managed correctly.