28-year-old Sandy Thi Nguyen of Aurora, Colorado was just busted for pretending her six-year-old son had cancer . . . accepting $25,000 in donations from the community . . . then using some of the donations to take her family to Disneyland.

Sandy even convinced her son that he had cancer and was dying.  The rest of her family believed it too.

Finally, 10 days ago, the sheriff's office figured out something suspicious was going on and investigated.  They found out the kid never had cancer and it was all a scam.

They recovered $23,000 of the $25,000 in donations when they searched the Nguyens' home on Thursday.  Sandy was arrested on two felony charges, theft and criminal impersonation to gain benefit.