The biggest stars on the Boston Bruins teamed up for the kids on Monday -- busting out their best costumes from 'Toy Story' to spread some Halloween joy at the Boston Children's Hospital and the pics are awesome!

Superstar David Pastrnak -- who's leading the NHL in scoring -- put on his best Rex costume ... along with Brandon Carlo (Hamm), Charlie McAvoy (Toy Alien), Charlie Coyle (Jessie), Danton Heinen (Woody) and Torey Krug (Mr. Potatohead).

The kids were STOKED to see the hockey stars roaming the halls -- where they gave out high fives, hugs and selfies to kids of all ages!

The families were happy too ... because when your kid is stuck in the hospital, seeing them smile is the best thing ever!