Steps to check for duplication in child.

[aba]

There may be situations, where you might be required to do duplicate
check for data entered in the child. For example adding team members
to a team......

Step 1: concatenate ";" before and after the cell content in question
in child template [=CONCATENATE(";";B4;";")]
Step 2: take it to parent [=CONCATENATE(Sample_TeamMembers_1.B12)]
Step 3: Bring the contents of the cell created in Step 2 back to the
child template [=Sample_Team_1.G22]
Step 5 : Search for the contents of text created in step 1 in the text
that you have in step 3 and then move the cursor position to end of
the found text. [=FIND(B12;B13)+LEN(B12)]
Step 6: Now split the text in step 3 from the position obtained in
step 5 and take the second half of the text. [=MID(B13;B14;LEN(B13)-
LEN(B4))]
Step 7: Now search for the text in step 1 in the text obtained in step
6. if the output is zero then it is not a duplicate value, if the
output is greater than zero then there is duplication.
[=IF(LEN(B15)>=LEN(B12);FIND(B12;B15);0)]

i have attached the model (Team) in the files section. have a look at
it to see it at work........