I so excited that you really enjoyed the Start Up. Amanzo4jc really summed it up well.
I just had some additional thoughts.
Anytime you are creating themes or thinking of games you want to play with your child the very first thing to start with are your child’s motivations. It sounds from your message that he really enjoys letters, using his hands and barnyard animals.
Then next thing to consider is what skill you want to help him grow in. You can gain great insight by reviewing the Social Developmental Model http://www.autismtreatmentcenter.org/fi ... -model.pdf
. We recommend consider only a few goal at a time. For example, maybe for the next few month you will really work on eye contact to start and continue the interaction, lengthening his interactive attention span, and clear single words.
When designing your game imagine yourself having so much fun presenting the game, showing him how it is played, giving him a lot of what he is motivated for and then inviting him to participate within one of his goals.
Here is an example of how simple it is. One motivation is for letters. Maybe a goal in mind is lengthening his attention span. Bring in big colorful alphabet letters to the playroom. Make a silly song for each of them. Hang them from the ceiling. When he looks at you grab one letter and sing the song representing the letter. All you have to do is entertain him with your song and dance. If he is still captivated for a few minutes then give him another role of pulling down the next fun letter for you to sing.
Have fun in all of your presentation and remember to celebrate all of your son’s participation (e.g. Eye Contact, Physical participation, language, etc.)
Have fun and post any questions you may have.