@sholay2011 I'm also an Asian polyglot but live in Colorado. I quite regularly speak in Spanish with my elementary-aged adoptive mixed-race daughter in public. She doesn't look Asian or especially Hispanic, but it's a part of our family's heritage. My wife is Basque and my Chinese family of origin has become quite Hispanicized over the generations since my ancestors arrived in the United States.
We also speak snippets of my native Cantonese at home (my wife and daughter have both picked up a bit from me), though I haven't managed to pass quite as much of that along mostly for the sheer lack of other native speakers around with whom we can practice.
The Spanish does sometimes occasion a double-take from folks at the sheer mental incongruity, but I've found that for my very multiethnic family at least, sharing a foreign language in public does help to cement the idea in folks' minds that yes, we are actually a family—especially if it happens to be just me and my daughter out and about.
In truth, most onlookers are just curious or a little surprised rather than hostile. Over the years, we've managed to randomly connect with a few friendly abuelas who noticed and appreciated that our rather family shares their native tongue and occasionally help more recent immigrants with impromptu translations in a pickle. I wouldn't give up these formative experiences for my kid for anything.
The few that just stare or give you a hard time though, they can vete al cuerno! From my perspective, language and culture are intangible treasures that we've received from our elders and truly deserve to be passed into the hands of future generations—just as much as a monetary inheritance from a grandparent's will. Your kid would be so much more impoverished to not have knowledge of Spanish—especially in a place like SoCal. And just for the sake of a few benighted and likely racist randos' opinions?! Let them pound sand.
If you can, strongly consider putting your kid into a school that's predominantly Spanish-speaking and Spanish-friendly as they grow up. Continued exposure outside of the family matters a lot with continued language acquisition and the normalization of speaking Spanish. There's already plenty enough of pressure to conform to only speaking English in the community. They don't need that at school too.
You shouldn't have a hard time finding a school like that especially in Southern California. I mean, I'm an A2 speaker and am already learning a fair bit of additional vocabulary and having my poor grammar occasionally corrected via my daughter picking it up from her classmates and teachers.
Having grown up in Southern California myself, I really think the reaccs that you get might vary depending on what parts of town you're in. I grew up in Lincoln Heights in Los Angeles and you'd occasionally run into Asians there who spoke Spanish as the local lingua franca. It wasn't commonplace but also not so rare that it'd be a spectacle. Maybe in other "paler" parts of SoCal?