Kids 16inch bike rear axle spacer question.

Hi there,i recently bought a 2nd hand ridgeback mx16 bike for my 5 year old.
When I tighten the rear axle it makes the freewheel bind.
I've noticed that it seems to be squeezing the frame in too much so I'm guessing its missing a spacer or washer on the internal side.
It currently is just cone and locknut on both sides.
Does anyone know the size of the spacer if there is one or by miracle does someone own this bike and could take a look at the setup on the rear axle.
Its actually missing the 2 rear big nuts that hold the wheel on so I'm guessing its had stabilisers on at some point.
Thanks in advance.