The Journey towards Collecting Stamps begins after your starter kit comprises of 20 stamps both US and Foreign arrives in the mail.
My recommendation is you purchase a stockbook. A stockbook is a similar to a photo album but its pages are slotted for various sizes of stamps. The book is neutral (not dedicated to a certain country or theme) and will permit you to store the stamps safely until you decide what type or topic of stamp you may want to pursue with your child.
The following are but a few examples---(upon receipt of your starter kit you might decide to stick with)
Certain Countries (i.e, France, Germany, Poland)
All Countries (i.e. the whole world of 150 plus countries)
Certain Themes (called Topicals, i.e, Shells, Fish, Butterflies, Soccer, Planes, Space, etc.)
If you decide to select the United States, then a US Stamp Album is a excellent choice to forever bound your stamps in a permanent collection. You will need a few low-cost supplies to start:
hinges: tiny adhesives that stick to back of stamp and album page
tongs: a type of blunted tweezer to safely handle stamps
magnifying glass: to increase your insight into various designs on stamps
mounts: a type of page protector but sized for stamps (best utilized on unused stamps)
You might not want to go this route so suddenly and just simply use a stockbook to fill with
US and various Foreign Stamps. If you do, you wont need any supplies other than the tongs
for handling stamps safely and possibly the magnifying glass.