Is this size bag suitable as 5kg hand luggage? (photo link)

[Damonlufc88]

Sons school bag, just thinking it is handy size to use at the beach aswell. Will be hopefully taking another backpack similar size

imgur.com/gallery/p4rECej

It's quite small. You could probably get away with a bigger one

Does it carry what you need to take on the plane? If you don't need a bigger bag, stick with it.

Presumably you also have hold luggage too?

It depends on what you're putting in it. A bag of feathers is far lighter than a bag of rocks.

(Not suggesting you take either!)