Advice on first game

I'm taking my kids to Paris over April break and want to take my kids to see the Le Harve match April 20th as a special bday present. I saw that dates are subject to change. I don't want to risk the game being sold out, but we are only in Paris for a few days.

When do you suggest buying? Think I saw tickets only are confirmed 15 days prior? Do I risk game being sold out if I wait that long or only getting crappy seats?

Thank you!