AirTags have batteries. They are good for about a year. Unfortunately they still depend on iPhones/iPads to detect and report location over any meaningful distance - this device is intended for use in large, outdoor areas (to minimize location inaccuracy) like music festivals or big outdoor sporting events.

This device claims 24-36 hours per charge. Actual specs are on the "preorder now" page. Claims 35g weight and dimensions of 50 mm diameter and 15 mm thickness.

I could definitely see families buying these before a theme park trip. Compared to the total cost of a Disney trip for four or five, $200 (4 @ $50) or $235 (5 @ $47) is a drop in the bucket.