What Magistal solution can we make for a 6-year-old child with huge sweat hands?

It is not easy to answer this question. Something for a dermatologist! I suggest you start by reading the text on the website Bassron under Glycopyrrolate. This substance is widely used in the US both orally and externally. Maybe she's cheaper there? In Belgium There is a speciality Robinul, which contains this raw material. From glycopyrrolate a syrup could be made:

R/Citric acid, glycerin, natural and artificial cherry flavor, methylparaben, propylene glycol, propylparaben, saccharin sodium, sodium citrate, sorbitol solution, and purified water. You can optionally use a mixture Ora sweet-Ora plus 1:1.

For external there is AlCl3 solution see TMF but use a weaker dosage only 20%. Or AlCl3 20% in Hydroxyethylcellulose or HPMC gel. Better than the chloride is the hydroxychloride. Less acidic but no intervention RIZIV.

Scopolamine in ointment is also used

I hope you can help the patient here.