I have been to both many times:
Fun little mountain. They have great terrain and some really nice tree runs. I also believe they have a park but its rather small. I stayed in the cabins about 15 mins from white pass and that was a blast.
Also a fun little mountain. They have some killer pillows that are usually up all season if they have enough snow and you are willing to hike a little.
However having said all this, I would recommend Mission. If you stay in Wenachee, you can choose between Mission and Stevens, and although i do love Mission; Stevens is a much much better mountain than both of these ski hills in every way. My advice: convince your parents to rent a cabin at lake Wenachee and then you can ski both resorts.
Stevens Pass and Mt. Baker mo fucka