Data gathered by the BBC reveals demand for abuse imagery has shot up.
Reports of obscene online material more than doubled globally to more than four million between March and April.
The US-based Center for Missing and Exploited Children said some of that rise related to one especially horrific and widely-circulated video.
In the UK, where 300,000 people are considered a threat to children, there were nearly nine million attempts in the last month to access child sexual abuse websites which had been previously blocked by the Internet Watch Foundation.
The anti-child abuse charity, which reports sites to internet service providers, says that since the lockdown began there has been an 89% drop in site deletions by the tech companies.
It believes this may be because many of these firms have fewer people staffing their hotlines during the pandemic.
Spanish National Police say reports of online child sex videos leapt by just over 20% since just before the lockdown there began on 13 March.
Their counterparts in Denmark revealed the number of attempts to access child abuse websites has trebled.
With most schools closed, children are spending more time online. Experts say that puts them at greater risk of grooming for sexual abuse.
Cathal Delaney of Europol told the BBC: "Children are more vulnerable, they're isolated, they're not being as well supervised online and they're spending more time online during this period than they would have previously.