We've been invited to attend a First Communion. Etiquette question?

[Leslie D]

Our 8-year-old son was invited to attend the First Communion of 2 kids (fraternal twins) that he once went to school with. We are honored that our son was asked to attend, but not being religious ourselves, we're not sure what is customary here. We definitely don't want to accidentally do the wrong thing. Do we bring a gift? If so, we're at a loss what type of gift it should be: the type of thing you'd bring to a birthday party? Since we don't share this family's faith, I'm not sure we could really offer anything that has religious overtones, but we'd still like it to be meaningful. Does someone have a suggestion?

And what is appropriate to put on the card? "Happy First Communion" just doesn't sound right, but again, I just don't know how it's usually done.

Any suggestions would be appreciated!