Brainpop Jr. lists itself as online animated educational movies for grades K-3, but really is a lot more. Falling into six categories (science, social studies, writing, math, health and reading) each lesson has one or more videos, games, a comic strip called "belly up", an interactive word wall, two level of quizzes and talk, write, draw and read about it sections for extension activities. All of this in addition to teacher guides and ideas for classroom activities. The videos are even close captioned if you chose. The site is touch screen accessible to a degree (excluding the write about it section unless you use your own onscreen keyboard), but is not switch accessible. The content is relatively age appropriate even for older developmentally delayed students - there are no cutesy elements or babyish images. Brainpop Jr. is constantly adding new content, so sign up for the e-mails that tell you what has been added.
There is, of course, a Brainpop Sr., but it is $175 for a single teacher for a school year (as opposed to Jr. being free - at least for now).