How do you know it is safe long tern ? This is polyethylene glycol that your kidneys might not like long term.
I wouldn't take it at all if I were you - it has a bad rep for addictiveness/side-effects. See this link for more info:
http://health.groups.yahoo.com/group/Miralax
I take it everyday (Well most anyways) and I'm 13 it's very safe.
My son's doctor has him take a dose daily and he is only 14. So it can be taken daily.
Yes, it's very safe and non-habit forming. It is only a stool softener, so it can be used indefinitely.