Yes some airlines do seat families apart but if the child is under 13 then the child will be seated next to one of the parents.
If the child is 13 or older then they might be seated farther apart depending on the seating assignments.
Every time I've flown on the airplane kids older than 13 were usually seated a few rows down from the parents and they will try to have them seated as close as possible to the parents.
But sometimes they might need to sit farther apart which is okay and kind of nice even though you love your kids sometimes it's good to be apart from them on the plane so they have their time alone and we as the parents have our time alone.