Is this backpack too small for a (nearly) four year old?

[Lemonylem]

www.my1styears.com/personalised-car-print-backpack.html

Help! I’ve ordered this for my friend’s little boy. It’s just arrived and is lovely but I’m panicking it’s too small. I don’t have any kids so have no idea what would be right!

Link doesn't work.

I'm sure it would be fine for a school PE kit.

Too small for what? How can a bag be too small except in relation to a specific item that one is trying to place in it? Presumably this is a (beautiful and lovely!) gift , not a receptable for a particular item the 4 year old has specificied?