OUTINGS with 3 small children, Autism and only 1 parent

Outings are the HARDEST for me, not only do I have 3 small children, BUT its only ONE of me and THREE of them! Then there is also Autism, which limits at times where I can go with all three kids to be able to keep up with all three. At times Kaitlyn is like 3 in 1! I cannot keep my eye off the kids, and specially Kaitlyn because she will WANDER off, she will RUN off, and she is not able to sense any danger around her. So if we go to the park, if I am pushing another kid on a swing, Kaitlyn can run off and a stranger can just pick her up and leave, or she can run into the parking lot or even worse into the street, those are my biggest fears, and if i just keep my eyes on her, the same can also happen to the other two kids.  I get invited to events, birthday parties, and even play dates. A lot of the time, if I know people wont understand why our family is different, or understand why Kaitlyn is different. I don't go. I don't go if I know I cant control the situation and its more of a hassle to go for the kids and me than for all of us to just enjoy it. So if I ever cant attend something you have invited me to with the kids, please dont think its because I'm being rude or dont want to hang out. Our family is a lot different than your typical family.