As dragonchild rightly points out, you leave us guessing about the parent-child relationship, but assuming that a "child" is defined as being identical to a parent but with a suffix of /_\w+/, and also assuming that "children" will not appear in the list unless a matching parent also appears in the list, you could start with the following code.

use strict;
use warnings;
use Data::Dumper;

chomp (my @family=<DATA>);

my %parents;

for (@family) {
    if (/(Test\d*_\d+(?:\.\d+){3})(_.+)/) {
        push @{$parents{$1}},$_;
    }
}

print Dumper(\%parents);

__DATA__
Test_100.26.35.6_1
Test_100.26.35.6_13
Test2_9.25.6.27_2
Test2_9.25.6.27
Test_100.26.35.6
Test_100.26.35.6_10
Test3_28.20.116.210_ide
Test3_28.20.116.210
Test4_28.25.6.21_45
Test4_28.25.6.21_45_25
[download]

Output:

$VAR1 = {
          'Test3_28.20.116.210' => [
                                     'Test3_28.20.116.210_ide'
                                   ],
          'Test2_9.25.6.27' => [
                                 'Test2_9.25.6.27_2'
                               ],
          'Test4_28.25.6.21' => [
                                  'Test4_28.25.6.21_45',
                                  'Test4_28.25.6.21_45_25'
                                ],
          'Test_100.26.35.6' => [
                                  'Test_100.26.35.6_1',
                                  'Test_100.26.35.6_13',
                                  'Test_100.26.35.6_10'
                                ]
        };
[download]