This last house in the culdesac is 19876 Collins Road. A search seemed to mark that address at the second-to-last house.

Unable to answer "What kind of building is this?" for osm.org/way/413227711 via StreetComplete 50.1:

Looks more like a small asphalt lot, no building

"Church"
OSM snapshot date: 2025-01-21T15:15:53Z
POI has no name
POI types: building
#organicmaps android

onosm.org submitted note from a business:
Name: Universal Movers Santa Ana
addr:housenumber=2500
addr:street=2500 Red Hill Ave #204
addr:city=Santa Ana
addr:postcode=92705
Phone number: 7144753922
Website: http://universalmovers.net
Opening Hours: Open 24 hours
Wheelchair accessibility: yes
Category: Transportation
Description: Universal Movers LLC is a registered business with trademarks in the Bay Area, San Francisco. We offer high-quality service to local and long-distance customers, with exceptional support throughout the relocation process. Request a free quote today!
Accepted payment methods: Cash,American Express,Visa,Mastercard
takeaway=yes

2590 Redhill Avenue, Santa Ana, California

This address is missing unfortunately. The apartment Complex is title Broadstone Atlas. Information for the apartment and its neighboring sister apartments Broadstone Arden, Broadstone Archive can be founded here for confirmation on how valid this information is.
Atlas:
https://broadstoneatlas.com/

Did they ever open this as a splash pad or repurpose it as something else?

Do the concrete paths connect under the trees?

onosm.org submitted note from a business:
name: The Simon Law Group
phone: (310) 914-5400
website: https://www.thesimonlawgroup.com/
twitter: undefined
hours: M-F 8:00 am - 5:00 pm
category: ,Personal Injury Law,Lawyers
address: 1327 North Broadway, Santa Ana, CA

Add Santiago Hills community marker for area surrounded by Newport, Chapman, Jamboree, and Peters Canyon

East Avenida de Santiago, Anaheim; "no stopping anytime" signs on street. Pedestrian access only?