The following options don't require a subscription or fee to watch cartoons online, although some of them do have subscription-based models that viewers can choose. In these cases, a subscription will get the viewer more options than the free version, which often includes commercials.
1. YouTube
This one is pretty obvious, but some cartoon fans might not know how extensive the YouTube library actually is. While it hosts uploads from all kinds of accounts, many of the big animation studios and platforms have their own channels on YouTube, which you can subscribe to (for free) and watch.
YouTube also has paid options for music and TV streaming, which will allow more options and not require viewers to sit through ads.
2. PBS Kids
Good ole PBS still has a lot of great, free programming — especially kid-themed — and this includes cartoons. There are lots of classic shows to watch, as well as newer titles that your kid (or you) might enjoy.
PBS gets public support for its content, but it also offers subscriptions for some of the material it offers. Check with your local affiliate to see what kind of programming is available in your area. PBS Kids is their web-based platform, and all you'll need is an internet connection to watch online.
3. Pluto TV
Pluto TV is a video streamer with a respectably large catalogue of animated shows, probably including some of your favorite cartoons. Like many free options, it relies on ad revenue, so you'll have to sit through commercials.
Although Pluto TV is similar to traditional TV, with a steady stream of "live" content you can browse, it also has an on-demand option.
Both can be accessed through a browser, making it accessible on computers, smart phones and tablets. And like pretty much all of the options on this list, it also has an app you can load on your smart TV.
4. Tubi
Tubi is a streaming platform with lots and lots of options for cartoons. Like many free streaming platforms, it doesn't have a fixed catalogue, so shows will come and go, which necessitates some browsing on the part of the viewers.
Be aware that the free streaming comes with commercial interruptions. Tubi's collection at any given time is enormous, in terms of different genres and individual shows, so if you don't mind some ads you'll have plenty to choose from.
5. Cartoon Network
Cartoon Network, like so many other mainstays of cable, has also updated their platform to keep pace with the changing times. They have their very own app and website for streaming (through the Max service, listed below), where you'll find lots of options.