I wondering can you advice me what to do and what brand of dye colour? PLEASE.........

Any color would be good. Only plain baby blue is considered too boyish. Even a bright blue is fine. You'll get nice purples if you over-dye a blue garment with fuchsia. Anything but orange is good. (Orange plus blue makes mud color.)

It is best to use fiber reactive dye. This is safer for babies' skin than all purpose dye, because it bonds much more tightly to the fiber. It also lasts much longer. (Don't buy "all ourpose" dye unless you are dyeing nylon or wool.) I recommend that you order a "tie dye kit" from a company such as http://www.prochemical.com or http://www.scarletzebra.com, possibly with some additional dye from their PRO MX dyes in whatever your favorite color is.

For the price of a single nice baby outfit, you can dye a whole wardrobe of baby clothes! That's what I did, for my babies.

You should also see http://www.dharmatrading.com for their adorable little white dresses and outfits to dye. If you buy Procion MX type dye from them, I recommend you avoid their "fuchsia" and substitute their "light red", as the color is very similar but the dye is easier to dissolve and therefore more reliable. People have been reporting problems with Dharma's Fuchsia.

Be careful not to breath any of the dye powder when you mix it up. A dust mask is a good idea.

The easiest method for dyeing is low water immersion dyeing - see
http://www.pburch.net/dyeing/lowwaterimmersion.shtml
- though I do love tie dye on babies, too.

Your older kids would probably love to have some shirts re-dyed in their favorite colors, too.