Playtime leggins, what size to make?

I am starting on my ten year old son's Dead pool halloween costume. (his chioce which I am not fond of but he is excited). I am ysing the leggings pattern for his super hero pants and I am a bit stumped on what size to make. I want them snug but not tight and most certainly not loose fitting. His measurements are 25" waist. Should I make him the size 8 or 10? What size should I use? I only made these for my daughter so i am not really possitive what size to go with.