In literally hundreds of trips to DL (and one to WDW) with a stroller in the past 13 years, I’ve had my stroller moved by CM’s maybe twice and never had one stolen. I don’t bring a “cheap” stroller, I bring what my child is comfortable in and what is appropriate for the day’s activities. Sometimes that’s a BOB, sometimes a double (ugh!) and sometimes a nice umbrella with plenty of shade, padding and comfortable handles. What’s the point in having a stroller that is comfortable if you are afraid to you use it, that’s what it’s for! However...
1- I have and will NEVER leave an infant seat attached to a stroller parked at an amusement park - how would you get home if your car seat was stolen? That one makes me nervous!
2 - we make ours very visibly identifiable and personalized. I have red and white polka dot ribbons knotted on my handlebars, and a big luggage tag with our name on it hanging from the frame just below. It stands out quickly in a crowd and someone looking to steal will likely pick something more discreet.
3 - I never ever never leave a single thing in the stroller other than maybe a water bottle. No bags, definitely no Disney shopping bags, no clothing, toys nothing. Often people will grab strollers and move them to another location to steal the CONTENTS, but want nothing to do with the actual stroller and will just leave it somewhere else in the park. This is where a Tile type gps tracker could come in handy, but they eventually end up at lost and found that night.
4- I have this silly habit of locking the brakes and backing my stroller in. More because I don’t want any little grubby germy paws of other kids touching it while Mom parks theirs. Also makes it much less appealing to steal, plenty of others with less effort.
5 - I’ve never locked mine but a friend locks her back wheels. CM’s will lift the back and roll it on the front.
6 - and probably the single most important thing you can do... Park it in the correct spot in the first place, as far back towards a fence or wall or rope as possible, park it neatly and considerate to those around you, and CM’s likely won’t have a reason to move it in the first place!