Advice on the internet: it's always worth the money. Just because I need to periodically revisit issues I've decided not to worry about, I recently read the post about the evils of W-sitting here.
If you're not familiar with the W-sit (be thankful) here's a picture of LB in a half-W, with leg and foot pointed back and away from her body:
For LB, and many other kids, W-sitting is a symptom of low tone and low core strength. Where kids with typical tone use their core muscles to stabilize themselves while sitting, kids like LB compensate for core weakness by making themselves as wide as possible while sitting. In our journey through the world of PT, we've encountered a couple schools of thought related to W-sitting.
One, like the author of the linked article, says that as kids W-sit they further weaken their core, and that W-sitting is a bad habit that should be corrected until kids no longer do it-and strengthen their cores so by sitting properly.
An alternate view expressed by two of our PTs is that the benefits of reinforcing correct posture are outweighed by the developmental harm of constantly correcting a child who is trying to concentrate and learn through play. Between ages 1 and 2, LB W-sat a lot and it was clearly her most comfortable sitting position. Her PT encouraged us to allow her to continue her activity while quietly pulling one of her legs straight so she was in a half-W. She also told us that she didn't consider it necessary to constantly correct a busy bee like LB, who was often in motion and shifting positions. So a kid who W-sits for short periods interspersed with other positions may not need the same level of intervention as a kid who is sitting in a W for a half hour while working on a project.
At LB's most recent PT evaluation, the therapist was even more emphatic that W-sitting is the symptom, not the problem. He recommended as much walking, running, jumping, swimming, etc. as LB can manage in order to strengthen her core. Encouraging LB to be active can be hard, sometimes she will absolutely refuse to walk, sometimes she wants to go to the park but only wants to go on the swings. And modeling physical activity and engaging her in games really helps, but B and I are also human beings who don't always want to play chase with a young child, so sometimes challenging LB to get stronger means challenging ourselves.
According to that PT, the goal is overall strength, and if you build strength W-sitting will decrease without a lot of intervention. I like that a lot more than viewing W-sitting as a "bad habit." Doing what feels comfortable for your body because your body is atypical is not a bad habit nor is it lazy (I also don't like the "droopy snowman" thing).
If we we're to get to a place where we felt LB needed more intervention with her sitting, I would much rather present it as a positive, "sitting this way helps your body get stronger," and get her some low blocks to sit on than present W-sitting as a character flaw.