Fields sorting question

Hi,
I have 2 simple views with lists of nodes. Now I add these 2 views to a parent view as fields. How can I sort these 2 fields by the post date of the nodes from the child views?

Node 1 - September 2|                                          |
Node 2 - some date    |  --- Child view (field 1)      |
Node 3 - - some date  |                                          |
                                                                               |  - Parent view
Node 1 - September  1 |                                        |
Node 2 - some date    |  --- Child view (field 2)      |
Node 3 - - some date  |                                          |

and after new post

Node 4 - September  3 |                                        |
Node 1 - some date    |  --- Child view (field 2)      |
Node 2 - - some date  |                                          |
                                                                               |  - Parent view
Node 1 - September 2 |                                          |
Node 2 - some date    |  --- Child view (field 1)      |
Node 3 - - some date  |                                          |

I would be very grateful for any suggestions!

Alex