Age 3: Stiles meets Heather in nursery school.
Age 4: Heather's family moves to the edge of town when he is four, but their moms are close friends who keep in regular contact even if Stiles and Heather don't see each other much anymore.
Age 5: Stiles meets Scott at age 5, in kindergarten, when he's on the school playground at recess. Jackson Whittemore is picking on Stiles and Scott stops him from stealing one of Stiles' shoes. They are instant besties. Stiles goes home the same day and informs his parents his has a brother named Scott and begs them to let him come over that weekend to play.
Age 6: Stiles mom initially got sick when Stiles was six.
-Claudia read Harry Potter to Stiles on a nightly basis before bed until she no longer could.
Age 7: Stiles and Scott decorated Stiles' bedroom ceiling with glow in the dark star and planet stickers. Scott fell off Stiles' dresser -- twice, breaking a couple of Stiles' Ninja Turtle action figures.
Age 8: By the time Claudia died, she no longer knew Stiles' name or who he was.
-After Claudia Stilinski died, Stiles became hyper-vigilant and concerned about his dad's health, as well as Scott's, because he'd seen Scott have asthma attacks before.
-Stiles memorized all of the police codes that the sheriff's department used so that he would know if his dad was in any danger while he was out on calls.
-After his mom died, Stiles spent an inordinate amount of time with the McCall's while Sheriff Stilinski tried to pull himself together because he was drinking and working a lot.
-Stiles' crush on Lydia started shortly after his mom died. He was crying at school and being picked on by a couple of other boys about it and she told them to stop and glared at them. That was when he realized there was more to her than just another pretty girl.
Age 9: Stiles had nightmares after watching the Child's Play movies.
-One night while staying with the McCall's, Rafael, while drunk, told Stiles to stop crying over his mom and grow up.
-Scott's parents had a huge screaming fight the results in Scott falling backwards down the stairs and getting knocked unconscious. Melissa kicked him out of the house. Scott called Stiles crying about it, and Stiles stayed on the phone with him all night, promising he'll never leave.
-While racing to see who could get to the top of a tree in Stiles' yard faster, Stiles fell and broke his arm and was in a cast for the summer.
Other Random Facts:
-Claudia Stilinski was born and raised in Colorado. She has one sister who still lives in Snowmass, Colorado. Sarah is Stiles' only living relative on his mom's side, but he barely remembers her.
-Claudia Stilinski was an avid gardener. She was also a baker. Stiles helped her in the kitchen a lot with baking while he was growing up.
-When Sheriff Stilinski was able to do long weekends, the three of them (and sometimes Scott) would go camping. Both elder Stilinski's enjoyed fishing.
-Jackson Whittemore bullied Stiles (and likely Scott) on a regular basis until Scott was turned into a werewolf. This bullying extended into actually stuffing Stiles into his own locker a couple of times when he was by himself.
-Stiles does know how to cook, and usually does so a few times a week to ensure that his dad is eating semi-healthy foods regularly.
-I do go with the idea that Search for a Cure happened for Scott and Stiles.
-Stiles writes college-level papers for profit and sells them online to desperate students. It's how he pays for random jeep repairs.
-Between S2 and S3 during the summer while Scott was in summer school, he and Lydia began spending a great deal of time together hanging out and researching. They grew to be actual friends during that time period.
-Up until the nogitsune possession, Stiles was very jealous of anyone who spent time with Scott, because Scott had always been his only friend.