Hi mphorsley - I would love to help and give you some suggestions for your classroom. It is so wonderful that you are focused on playing with the children in your classroom. We have seen that play is one of the most fundamental keys to helping children. When children are motivated, they are more likely to learn and grow - and they are more able to generalize the skills they learn when they learn those skills through fun and motivating activities.
I'd first like to suggest that you take advantage of the free resources on our website. I think there are so many videos that would really help you (and your assistant, if she is interested in watching them with you). There are videos on numerous topics - creating games, teaching language, helping higher-functioning children, etc. You can access our video library here: http://www.autismtreatmentcenter.org/contents/other_sections/autism-treatment-webcasts.php
I would also be happy to help you with specific questions on how to help your children via this message board - so feel free to post more questions any time you'd like.
To give you some suggestions to start:
1) Your focus on play and motivation is key. Help the children feel excited to play with you - by creating activities for them based on their motivations and interests. Kids love it when you follow their lead and make them the one in charge of what you're playing. Continue your focus on play and fun in the classroom - this sounds great!
2) One sure-fire way to create motivation for children is to celebrate them - for looking at you, for talking to you (even if they've talked to you before - it's still exciting that they're being social!), for interacting with you, for following your instructions... The list is endless - but the focus is clear - celebrate, celebrate, celebrate - kids love it! (You can quietly whisper your celebrations, sincerely share how excited you are, cheer in a big way, etc.)
3) And maybe you could even apply idea #2 to your assistant. I see every day that people really do the best they can with what is going on for them at the time. If your assistant has an inoperable brain tumor, perhaps she'd just really like to know that what she's doing is good. I'm sure you can find things to celebrate about her work and her time with the children. By celebrating her, you'll be building more of a relationship with her and maybe she'll be more open to following your lead in the future.
Wishing you all the best - and looking forward to your questions!