Cheshire Police is appealing for information and video footage after a "small minority" of Telford fans set off smoke bombs after their team scored at the Deva Stadium, in Chester.
Officers say two were thrown onto the pitch, while the third was ignited amongst the supporters and remained in the stand.
Afterwards it was reported that a nine-year-old boy needed hospital treatment for injuries.
Inspector Anna Galloway said: "One woman suffered breathing difficulties and was treated at the scene by paramedics, before returning to the stand.
"There were no reports to police at the scene of any further injuries. However, officers are aware of media reports relating to a nine-year-old boy and enquiries are ongoing."
She said officers were working with both clubs to establish who is responsible and to assist in seeking banner orders for those people.
“While the vast majority of fans were well behaved throughout the match, sadly there were a small number of fans who decided to ignite and throw smoke bombs.
“Throwing objects onto the pitch during a regulated football match is a criminal offence and we are working closely with both clubs to identify those responsible.
“As part of our investigation we are keen to hear from anyone who witnessed the incident or anyone who knows the identity of those involved along with anyone who may have video footage of the incident.”
Anyone with any information in or video footage is urged to contact Cheshire Police quoting IML 1160301.
A statement by AFC Telford on Sunday said: "Several flares were let off this afternoon by a small minority of away supporters which has resulted in a nine-year-old boy needing hospital treatment this evening.
"We will take the strongest action available against anyone found in possession of a flare, smoke bomb or any other such pyrotechnic device, and spectators are warned that we and the National League apply a zero-tolerance approach to anyone attempting to bring such device into any stadium when following AFC Telford United."
The club also warned that anyone found to have been involved will be banned from its New Bucks Head ground for life.