Brake lever shims for little hands

[Jayfish]

Having just bought Jr his first roadie, we're having a bit of a reach issue on the STI levers. I could rotate the hoods further down the drops the bring the levers in closer but we're already at maximum stretch as I've bought a bike he fits but has room to grow (rapidly!) into.
The bike has Tiagra 10 speed on it, 4600 afaik, and I'm having difficulty locating the correct brake lever shims to adjust the levers, plenty of same generation Sora ones and 105/Ultegra ones.
Ideally I'd like the correct ones but if other groupset ones are known to work I'll happily go with.
Anyone have any knowledge of the above or knows a man that does?

[richardxjr]

105s are about 30x22mm. The thicker ones bring reach in by 10mm.
Got some fresh spare ones I can pop in the post if you like?

Eta Sora with side cables are about 35x30
Argos bike shipped with bigger shims but mine went in the bin.

Edited by richardxjr on Saturday 6th September 08:13

[Jayfish]

Thanks Richard, excuse my ignorance but do the shims attach to the lever top or inside the hood upper and which piece would I be measuring?

[richardxjr]

Above the lever top (the lever rests against it when released). Rubber gasket either about 2 or 4mm thick, ish, triangular, push fit.

The thinner gasket might well be in place, for 5mm. It was on my new bike, and the new 105 shifters I just bought. The thicker one gives 10mm.