Yes, we used the area in front of the Haunted Mansion. Be sure to get a Special Assistance Pass at the Town Hall on Main Street or at Guest Services at DCA at the beginning of your trip, You can show this to a CM and they will assist you in getting to the protected area. The earlier you get there, the better. The nice folks in wheelchairs are usually quite happy to let little kids sit in front of them, as long as the kids do NOT lean on the chairs.
There are few seats available, I sugggest taking a garden knee pad to sit upon - it is very rough concrete there.
If you have any questions about the Disneyland Special Assistance Pass (known as the GAC at WDW) or taking kids with autism or other special needs ot Disney Parks, please click on the link in my signature and you will find links to information about making your visit easier and more fun.