What's the word limit here?
Ok, keeping it short...
I find kids/toy channel don't do much collabs, except at the high 1M+ sub level. Even then it's not very common. I guess it's hard to do collabs for many types of videos. The best would be 2 channels getting together physically and getting the kids filming videos together. Might be hard to muster though.
Content is very heavily trend influenced. Somebody comes up with something and a day later, sometimes a few hours later, there are exact copied. Some must live next to a Toys R Us!
Many viewers are very nice, and interact in the comments. We have many questions about the new baby, requests for videos, questions about age and stuff like that.
About 10% are haters. Mostly the hate comes from one particular type of viewer (can tell by their avatars). They should get out more into the sunshine!
Some channels I consider spam/scammers. They latch on to a few top channels, and pull tags, titles, video ideas and redo the videos. You can see there is no creativity, interest in the art, it's just a $$$ grab irrespective of Copyright law or respect or decency. it's ok to be inspired and recreate videos with your own flavor, perhaps reuse some tags and description ideas, but some take it way too far.
There is a lot of theft of videos (download and upload). Not sure of other verticals, but dmca takedowns take me several hours per week. I must have issued over 1000 already.
All in all, my feelings after 15 months full-time of this, is the channels in the kids vertical pretty much keep to themselves, follow trends closely, and many are willing to take a heavy dose of inspiration from trending videos.