The combined terms and conditions of 13 top apps including TikTok, WhatsApp and Zoom would take 17 hours and five minutes to read, a firm has estimated.
The documents contain a joint total of 128,415 words - longer than any one of the first three Harry Potter novels.
The longest was Microsoft Teams at 18,282 words - or two-and-a-half hours of reading time for many people.
In 2018, a BBC study found that several website policies required university education levels of reading ability.
It is not possible to use the services without agreeing to the terms.
Other long documents discovered by thinkmoney included Candy Crush (14,189 words), Twitter (11,022) and Facebook (8,588). The word count included both terms and conditions and privacy policies.
The shortest on the list was Google Meet with 4,717 words.
Privacy researcher Stephanie Hare said that both the length and language used in such statements made them difficult for adults and children to be able to make informed consent about what they were agreeing to - and the only alternative was to not use the app at all.
"Consent implies choice, but choice is not what's on offer. It is difficult, if not impossible, for most of us to work and live today without using a smartphone, computer and other devices that allow us to transact online," she said.
The EU data regulation GDPR states that communications to individuals about their data must be "concise, transparent, intelligible and [in an] easily accessible form, using clear and plain language, in particular for any information addressed specifically to a child".
Microsoft Teams does include a sentence in its terms asking children not to create an account if they do not understand the service agreement - but it is more than 1,500 words into the document.
Microsoft declined to comment.
Think before you click
Kate Bevan, editor of Which? Computing magazine, pointed out that both Android and Apple devices now signpost more clearly what permissions an app is seeking - such as access to a device's microphone, camera or location.
"When you install an app, take a couple of minutes to think about what it's asking to do, and if you're not comfortable allowing an app access to your contacts, for example, then think twice about whether you want to install the app," she said."It is important for businesses to communicate in a way that users understand."
At an event last year, Simon McDougall, a senior executive at the UK Information Commissioner's Office, described the "I agree" button at the end of terms and conditions documents as "one of the biggest lies on the internet".
"How many people are actually reading these things, how many are actually clicking, because it is quite scary how the muscle memory is building up as these hands are just clicking their way through," he said, as reported by the website IT Pro.