An Islamic State supporter encouraged "lone wolf" attackers to target Prince George and inject poison into supermarket ice creams, a court heard.
Husnain Rashid, 32, of Leonard Street in Nelson, Lancashire provided an "e-toolkit for terrorism" over the internet, the prosecution alleges.
He is accused of calling for the prince to be targeted at Thomas's Battersea primary school in south-west London.
Mr Rashid denies six terrorism offences at Woolwich Crown Court.
The jury was told that the former mosque teacher, who also used to work for a tyre business, ran a "prolific" online channel named the "Lone Mujahid".
He is accused of posting a photograph of the four-year-old prince, along with his school's address, a silhouette of a jihad fighter and the message: "Even the royal family will not be left alone."
He also allegedly advised a British terrorist in Syria named Omar Ali Hussain on how to make successful attacks, including bringing down "enemy" aircraft with lasers.
The court heard that Mr Hussain was the main person contacted by the defendant who had himself "made preparations" to fight for Islamic State abroad.
Other alleged targets he suggested included a Halloween Parade in New York and railway stations in Australia.
Prosecutor Annabel Darlow said: "His proposals were indiscriminate and made no distinction between adult and child, between members of fighting forces and civilians.
"His suggestions included injecting poison into supermarket ice creams and targeting Prince George at his first school."
Ms Darlow said Mr Rashid specialised in supporting lone attackers with "every conceivable type of attack" including the use of bombs, chemicals and knives.
He is also accused of distributing the al-Qaeda terror magazine Inspire, and allegedly wanted to travel to Syria to fight in Islamic State territories.
The court heard when police raided his house he "hurled" a phone containing a "treasure trove" of evidence over a wall and into an alleyway.
Mr Rashid denies three counts of engaging in conduct in preparation of terrorist acts, one of encouraging terrorism, two of dissemination of a terrorist publication, and one of failing to comply with a notice under the Regulation of Investigatory Powers Act.
The allegations span a period between October 2016 and April this year.
The trial continues.