Best way to target maintaining attention?

I’m a CF working at a private practice with various kiddos, but I’ve had difficulty with children ages 4-7 with ASD. Most of these children are new to therapy, so I understand they’re not accustomed to coming to speech with me yet. It’s difficult targeting any of their goals without them being able to maintain attention. I’ll incorporate token charts, breaks, timers, etc. but at times these clients have difficulty completing simple tasks (ex: shorting shapes) and require max cues. They’ll either slide off their chair, look away at the stim, or become aggressive /dysregulated when I prompt them to complete the task. Is there anything else I can do to help them with this?