Filtering GetChildRows

I have an xml file which has defintions for "event" elements. Each event
(currently) has 2 standard fields "id" and "name", and a number of custom
fields, the number and descriptions of which may be different for each
event.

An example file is below

<event>
<id>1</id>
<name>Event One</name>
<fields>
<custom1>Custom Value 1</custom1>
<custom2>Custom Value 2</custom2>
</fields>
</event>
<event>
<id>2</id>
<name>Event Two</name>
<fields>
<custom3>Custom Value 3</custom3>
<custom4>Custom Value 4</custom4>
<custom5>Custom Value 5</custom5>
</fields>
</event>

I can load this file into a DataSet and look at the "event" table. Taking
the first DataRow in that table (event one) I Call GetChildRows. However
The resulting table not only has the "custom1" and "custom2" columns (with
the correct values) but custom3, custom4, custom5 (with null values).

My question is, is there any way of filtering this so the only columns
returned are the ones specific for that event, eg custom1 and custom2.

Thanks in advance

Dan