How old is your son? I would focus on having her do activities that he enjoys together and for that it is important to give her plenty of information about his likes and interests. I would also give her lots of space to really use the world and materials around.
I teach English as a foreign language in Spain and have wished a zillion times when I've had kids classes that I could just take them outside to run around, play hide-n-seek, do messy art or science experiments, scooter tricks, whatever.... anything to make the language real and active instead of being stuck sitting. I had one private tutoring situation last year where I had the freedom to work more like this with a girl who was passionate about dance. We watched Youtube videos about different dance steps and styles and talked about them, she showed me all the steps to the routine she was working on and we put language to describing them, we looked at equipment and clothing, photos from past recitals etc. She was also really into iCarly (but in Spanish), so I would set her homework watching episodes of iCarly in English and then she would need to explain the plot. She would write down 10 new phrases or words from each episode or a part she didn't understand and the minute that they occurred (watching online here) and then we would go back and break down what was actually being said, write out subtitles, etc. Her brother was into football and scooters, so he would give me a rundown on every match, explain about different players and their abilities and life stories. With his scooter we would watch tricks on Youtube and he would describe what was happening and we would look up info about how to do tricks, he built his ideal scooter researching all the equipment online and presenting the "finished' product to me explaining why he had chosen each component. They were moving to China, so we looked up skate parks in the city they were moving to, watched short videos about life and festivals there, etc.
If you post some more info about your son, I can give you some ideas