Sounds like some boundaries definitely need to be established with your mom! She should ask permission to take your son to a religious event...
She's probably already bought him a new suit Did she think he would not fess up to you about it? Would she convince him not to tell you.
You must status back and let us know how it all works out.
Certainly sucks to be strapped for childcare. Leaves you little option. I know that feeling.
My daughter is 10 years old and she is going with her father. She asked permission to go. I asked her why she wanted to go and she said, "because I get to dress up and it is the shortest meeting of the year!" My husband and I also prodded her to see if she knew what it was all about and we realized she pretty much tunes all of it out. She had no clue what it was about beyond the fact that Jesus sacrificed his life for us so I guess she got the most important part of it