Wear coordinating (you can match if you like) clothes.
Solid colors or very light patterns (patterns tend to distract)
Wear colors that compliment you but don't over-power.
Denim, khaki, black, blue, grey, white (look good in color and b/w)
Green is kinda difficult 'cause it can clash with nature's green.
Red can work, but doesn't always change to b/w very well.
If you are outside barefeet (especially on the beach) are a must.
You could have a pretend picinic... or a real one with a little bit of food if you want authenticity and a possibly messy kid.
What is something you like to do together as a family? Try to incorporate that a little bit if you can, makes it personal.
I love denim overalls on kids, they can go with a shirt, without a shirt, with shoes, without shoes, color / b/w, it covers it all.
Have fun... if you are having a good time, it shows in the photos and they turn out better.