Child's sleep patterns

Im trying to gather information and opinions about children that continuously have a disturbed sleeping patten and primarily on sleep during the day. I am a teacher employed for a family that has a five year old where her sleeping routine is changed weekly. Actually there is no routine! The child I refer to slept at 9am last morning. She will be allowed to sleep until 7pm tonight then she will perhaps sleep at 10am tomorrow. Thats right AM. Sometimes she sleeps for 2 6 hour time periods broken thought the 24 hours time period. Sometimes she sleeps for 12,or 9hrs,or 7hrs plus a nap. There is NO routine,or consistency. Surly this is detrimental for her growing. Pls any info info or feedback would be appreciated.
K Tomren