Make use of basic DB concept, for this u need a "foreign key" field in Lease tabel and a "primary key" field in another table, and relate them in the graph. Now u can print a report whereas each Lease will Include a table of the associated Leaseitems.
Since you are using a portal to generate the child records, you shouldn't be having any issues with the key fields. Sounds like an issue with your layout's design or the found set of records that currently exist for this layout.
call upon related fields in Leases (summary)...
Is this a sub summary part? If so, make sure that you have sorted your records in the same order as specified in the sub summary part's setup. If you are using FileMaker 9 or older, switch to preview mode to see this report. Only FileMaker 10 and 11 can display this report in browse mode.
Make sure you perform a find or correctly use Go To Related Records in a script from your Lease layout to find the correct group of LeaseItems for a given lease. (Unless you want a report that lists records from multiple leases.)
If that doesn't get things working for you, please report back with a detailed description of exactly how this isn't working for you.