>The mantra is to cancel subscriptions to whatever you're not watching ATM, but with young children that's untenable
Young children don't need to watch TV, in fact it'd be better if they didn't watch any at all. Maybe have some DVDs they can watch when they want; that's certainly a lot cheaper than any kind of subscription.
Adults don't need to watch TV, either. I think society at large undervalues appropriate use of TV for kids. Kids crave structure, repetition, and music. With proper restrictions, TV offers all of that without requiring adults to put on the same dog and pony show every day. While studies show it doesn't help with speech, it can help reinforce concepts they are learning in other mediums; animals, objects, movement, emotions. As an adult, there's so much collective culture from TV and movies I consumed as a teenager that come up when interacting with other people.
I already mentioned I would much prefer to purchase outright, but kids tend to get into very specific things and a lot of things available for streaming aren't sold on DVDs; discoverability and availability. Another problem with DVDs is that they're fragile and difficult for young kids to operate themselves--not to mention I don't have a DVD player. I've heard a lot of parents get very angry that expensive Disney DVDs got scratched or broken, whereas VHS was a lot more durable and straightforward for kids to operate themselves.
Kids, young adults, or even having more than a few people in a house it's hard to say, "You can't watch Sesame Street like you did yesterday because Game of Thrones is over."
Young children don't need to watch TV, in fact it'd be better if they didn't watch any at all. Maybe have some DVDs they can watch when they want; that's certainly a lot cheaper than any kind of subscription.