I have to say that I am very lucky with our kids - they love each other and this is one of the biggest gifts in the life.
I used a transfer as a mask and clipped the biggest photo to it. Then I made the photo black and white with a Channel Mixer adjustment layer.
On the little photo I applied a free PS Action (Vintage Effect). I often use Actions - they can be easy to use and the result is very spectacular.

credits:
ANNA ASPNES
ArtPlay Palette Savor http://www.oscraps.com/shop/product.php?productid=33379&cat=383&page=1
Enjoy WordMix No. 1 http://www.oscraps.com/shop/product.php?productid=33378&cat=383&page=1
ScriptTease Life Overlays No. 1 http://www.oscraps.com/shop/product.php?productid=33376&cat=383&page=1
StainedGlows No. 1 http://www.oscraps.com/shop/product.php?productid=33375&cat=383&page=1

also used:
KrissKross Stitched Overlays No. 1 http://www.oscraps.com/shop/product.php?productid=30753&page=1
Taped Dotty Polka No. 1 http://www.oscraps.com/shop/product.php?productid=27150&page=1

Thanks for looking!
Eszter