What do magic bands do?

[ShotgunBetty]

I'm going to Disney soon and staying off-site. What exactly do Magic Bands do?
Can I use them to pay for things like food and souvenirs? Are there any other benefits?
I have a 4-year-old and a 2-year-old—are Magic Bands worth it for them?

 

[Charlie]

If you're staying off-site, magic bands are a nicety but unnecessary.

they allow you to make room charges, unlock your room (onsite only), tap into parks, rides, etc.
They also make noise and light up (depends on the one you get) but again nothing over the top IMO.

Save the $40 unless you just want to spend it, but I'd recommend using the money to get on property if you do.