Dozens of ghouls, goblins, zombies, princesses, cartoon characters — and at least one very convincing robot/mad scientist duo — descended on Massachusetts Street for the annual tradition of downtown trick-or-treating Monday evening.

Big Jay (Logan Dinges, left) and Baby Jay (Carter Dinges) take a short break from trick-or-treating downtown on Monday, Oct. 31, 2011.

Two-year-old twins Jax and Croix Kelley trick-or-treated as Dr. Seuss characters on Massachusetts Street Monday, Oct. 31, 2011.

Beverly Dick, owner of House Parts, 714 Mass., passed out candy for the third year in a row because she said it was “a really great way for families to get out” on Halloween.

The streets were packed from 5 p.m. until almost 7 p.m.

Here are the stories behind just a few of the costumes spotted early in the evening:

• Twin 2-year-olds Jax and Croix Kelley, with their blue hair and red jumpsuits, got attention as Things 1 and 2 of Dr. Seuss fame. Their mother, Shawn Kelley, said that they loved the “Cat and the Hat” and so it seemed like a logical choice.

• Jerry Campbell thought Jax and Croix’s costumes were some of the cleverest he’d seen. But his own 2-year-old’s was pretty smart, too — Etta Bea trick-or-treated as her nickname, that is, with wings, a black-and-yellow “body” and a fairy-like wand, she was Bumblebee.

“Her favorite part is the stick,” Campbell said.

• Logan and Carter Dinges are brothers and, respectively, dressed as Big and Baby Jay. Logan is older and says it was his idea to go with a Jayhawk theme

• Sarah Aistrup, who passed out candy in front of Genovese, 941 Mass., said that the best costumes she had seen were the “flock of baby chicks” — well, that was until a baby bunny walked by.

We’ll have more photos as the night continues. You can share your own Halloween stories with us in the comments.