Well, the Evil School System(tm) doesn't expect you to make proper costumes. They expect you to cobble something together out of trash bags, old curtains, duct tape and staples.

If you did make a beautiful authentic costume for MT#1, next year they'd expect you to make costumes for everyone. Because it's not fair if one kid has a beautiful costume and the rest don't.

It's a shame you can't all show up as a properly-dressed pilgrim family :D