I want to ask her on a date but need ideas

So I made friends with this girl named Skyla and her older brother Hayden. Hayden is autistic. How I met them was Hayden was kinda creeping me out staring at me and my friend at the mall, but he was just fascinated in my Lego shirt and wanted to tell me all about his Legos and Lego Hogwarts lol. His sister found him and apologized to him. I saw them again at the mall and Hayden was throwing a fit because he didn't wanted to go home and sat on the ground to cry so I decided to help and went and sat with him and let him show me his Legos on his phone. I became friends with them both and found out Skyla is bisexual. Yes! She said she doesn't really have any friends and relationships dont work out because they don't understand that her and Hayden are a package deal and she has to care for her older brother. Hayden is 25 and Skyla is 21. I absolutely adore Hayden. This boy is sooo sweet. At the park he kept picking me and Skyla flowers. So she doesn't trust a lot of people to babysit Hayden so if I ask her out he will obviously come. What dad can I do that's fun for all of us and will keep Hayden occupied? Also. How do I let her know it's a date even though we are bringing Hayden along?