We've seen lots of these threads over the years. Aside from sitting up front, some suggestions have been:
hanging out in the vestibule/out back
having a small bag of quiet toys/books that is ONLY for Mass and no other time (so its more desirable)
And, if all else fails - does your church offer nursery care and/or a preschool class during Mass? I generally advocate children being present at Mass, but I know how hard it is to manage little ones...