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Bonnie and Clyde's fame was actually very short-lived and soon turned into infamy, but during a time of economic sorrow, the public's fascination with this duo, stimulated by the publication of photos of their extravagant lives and the unfolding of their provocative story, gained them considerable notoriety.

On the 23rd of May, 1934, right after Parker and Barrow had been killed by the six lawmen that had fired around 130 shots at the Ford V8 they were driving, the car wreckage at the side of a country road gathered a crowd:

Bonnie and Clyde's fame was actually very short-lived and soon turned into infamy, but during a time of economic sorrow, the public's fascination with this duo, stimulated by the publication of photos of their extravagant lives and the unfolding of their provocative story, gained them considerable notoriety.

In the film, in Coffeyville, Kansas, the car and its inhabitant, having parked behind a drug store, are being recognized by a young woman, who immediately fetches her friends. Soon the place is crowded with young people, a "goddamn fan club", who apparently want their picture taken with the famous couple. I believe this is the scene you refer to in your question.
While Bonnie and Clyde were, like any fad, popular for a while, there is no record of this or similar events happening, and the whole situation seems highly unlikely to me. The Highwaymen makes use of artistic freedom to dramatize the story, and Hamer and Gault never actually ran into Bonnie and Clyde until the very end.

On the 23rd of May, 1934, right after Parker and Barrow had been killed by the six lawmen that had fired around 130 shots (167 according to other sources) at the Ford V8 they were driving, the car wreckage at the side of a country road gathered a crowd:

However,

[e]ventually, the cold-bloodedness of their murders opened the public's eyes to the reality of their crimes, and led to their ends.

[..] the massive negative publicity increased the public clamor for the extermination of the Barrow Gang.¹

The fact that Bonnie and Clyde robbed banks during the Depression's bank panic garnered them some popularity:

Several criminals operating during the Great Depression, including Bonnie and Clyde, became famous as “Robin Hood” figures who struck back against the banks that many considered to be oppressive.³

But the "ten or so"¹ banks they robbed were often small rural banks, and their gang actually preferred to rob funeral homes, shops, and gas stations along backwater streets, thus targeting small local businesses.

Eventually, the cold-bloodedness of their murders opened the public's eyes to the reality of their crimes, and led to their ends.

[..] the massive negative publicity increased the public clamor for the extermination of the Barrow Gang.¹

Bonnie and Clyde's fame was actually very short-lived and soon turned into infamy, but during a time of economic sorrow, the public's fascination with this duo, stimulated by the publication of photos of their extravagant lives and the unfolding of their provocative story, gained them considerable notoriety.

Bonnie and Clyde's fame was actually very short-lived and soon turned into infamy, but during a time of economic sorrow, the public's fascination with this duo, stimulated by the publication of photos of their extravagant lives and the unfolding of their provocative story, gained them considerable notoriety.