You heard it right from the Fireman's Mouth...
There is no effective way to enforce laws regarding Fireworks in Grand Terrace.
There is no truly Safe Firework, all Fireworks can start a hill, house or hair on fire.
Grand Terrace does not have enough law enforcement to cover and enforce the law, and to use Firemen to enforce the law would be sending unarmed personnel in to possible harms way. (Often the Fireworks, are being flamed by people who are also lit.)
If the City wanted to help folks raise money responsibly, perhaps they would host a watermelon picnic/fundraiser at the park. Or perhaps they could ask their "sponsors of GT Days" for a Youth Activity Fund equal to that spent on a one day party.