Hi and welcome

it really is impossible to suggest doses at it depends on age, and weight as well as individual's specific needs. usually best to check with a qualified professional on dose in a young child

generally over 12 yo/100 lb can take adult dose, half dose 6-12yo and 1/4 dose under 6yo

I documented what helped my son, but not everyone has the same requirements, although extra magnesium does seem to be needed by most people with TS and there is current feeling that it may be better not taken in conjunction with calcium

have you heard of Kid's Calm ionic magnesium supplement. I have heard very good reports on it calming tics in young kids. My son, now 19yo, takes the Natural Calm version each night and it really helps promote restful sleep as well.

The Epsom Salts (magnesium sulfate) baths are another real help for tic relief