It happened in the Whitleigh area of Plymouth on Monday night.
Police say a cordon will remain in place at Lewes Gardens, after a child sustained serious injuries on Monday night (23rd September).
Officers were called to the area at 9.30pm.
A 12-year-old boy was taken to Derriford hospital with serious injuries.
A number of "devices" were seized after searches by officers and the Royal Navy EOD team.
A Police spokesperson said: “Searches are expected to remain ongoing over the next two to three days in relation to this matter.
“I’m keen to provide reassurance that there is no risk to the public and that there is no evidence to suggest that the incident is linked to terrorism.”
A 16-year-old boy from Plymouth was arrested on suspicion of possession of an explosive with intent to endanger life. He has since been released under investigation pending further enquiries.
A 64-year-old man from Plymouth was arrested on suspicion of making/possessing explosive with intent to endanger life. He has been released on police bail until 23 October.
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