Our sons both started off in CYO. CYO is great place to learn the basics but a lot depends on the quality of the coaches/parents. In that age group for CYO, believe they play 7v7 and each player must play a minimum of 2 quarters.
Our kids rapidly outgrew the talent level at CYO and wanted to play soccer year around. Both our kids (8 and 6) now play for SA City FC and have for the last couple of seasons. Definitely a higher level of commitment, timing and financially, but the coaches and facilities are fantastic. They have 3 different locations - Great NW, North, and East. So depending on where you live or work should be able to find something convenient.
Let me know if you'd like some additional information and I'd be happy to provide as much background as possible.