There are many activities that teens can indulge, which would make them a role model for their younger siblings. Some of the ways are:
Eat healthier (fruits and vegetables), children tend to do what they see in their surroundings, eating healthy will encourage the younger siblings to follow the same footprints.
Play more outdoor games, due to technology, the trend to play outdoor games in our recent generation is drastically dropping. So, if teens are indulging themselves in physical activities, it will motivate the younger siblings to play and adopt a healthy lifestyle