How to get field value of Parent item type in Child Item type in relationship.

HeLLo Friends,

I have two item type

(1)Timesheet

(2)Task

Task is related with Timesheet as No Related relationship.

Both of Item have Property Date [ Data type : Date : date time ]

Now when user create the instance of Timesheet user will add instance of task as well.

can i have some validation on Child item [ Task ] that user can not enter date apart from the date selected in Parent item type [ Timesheet ]

Note : Here instance of Timesheet is not saved yet so id is still in memory only.

Thanks in Advance :-)