A 13-year-old boy on an electric scooter was seriously injured in a crash with a van, police said.
Another boy, who was riding on the same scooter, escaped with minor injuries after the accident in Bognor.
Sussex Police said: “Police are appealing for witnesses after a serious collision on Corbishley Road, Bognor, at around 5:20pm on Tuesday 21 October.
“Two people were injured.
“Is it reported that the boys, aged 12 and 13, were riding together on an electric scooter when they were involved in a collision with a white van.
“The 13-year-old boy remains in a serious condition in hospital.
“A further 12- year-old boy sustained minor injuries.
“The driver of the van was uninjured.
“Police are appealing for further information and footage as inquiries continue and we ask witnesses to contact police.
“If you have any information to report, email collision.appeal@sussex.police.uk or call 101, quoting serial 1118 of 21/10.”
