Common misconception in fantasy in fantasy or sword related genre. A sword is not heavy. Judging by the size, that sword is probably only 2 kg and most of the weight is not on the blade but on the guard, handle and pommel. So it shouldn't be hard to lift and swing it, even for a child
A sword isn't heavy. For an adult. And even then untrained people get into trouble after taking a couple of swings.. Stamina, y'see....
Same for Armour... 15-20 kilos distributed is ... not that heavy.. But it throws off your balance and makes you ..sluggish.. in your reactions if you're not used to fighting in it. And again... that Stamina thing....
One of the fun things as a re-enactor is letting kids, and occasionally adults experience this..
Which is why on the events that allow it, I have a little Arena and a pell... So kids can
feel things...
(and why I am continuously polishing paw prints off my gear....

Ah well... Take One for Team Edumacation...)