I heard there was actually some minor drama this last Reitaisai from fans that are parents(?!) that brought their kids and the R18 material was not separated enough from the usual stuff.
So even though ZUN and the fandom usually don't care too much, that might be shifting.
Certainly.... the*sigh* R-18 and Adult *sigh*be Touhou or beyond, Reitaisai or beyond, ought to always already be within, or appealed to be encompassed and encompassed, a "a separated and exclusive, or more separated and exclusive, area plus access/exit with definitely clear and helpful. warnings+explanations+checking...
The few games that have been released officially on consoles have been rated T, due to various things like the depiction of alcohol and smoking, and having the final boss fight literally take place in the middle of a giant lake of flaming blood. In general though I think Touhou is pretty family friendly, if not necessarily geared towards children. It's nothing that kids weren't raised on in the 90s and 2000s, and with a few minor exceptions the series is as chaste as it comes with fanservice. About the only thing I think people might find objectionable is the strong implication that Reimu and Marisa were underage drinkers in the older games, but that's something you just have to take or leave.
Based on
https://www.esrb.org/ratings-guide/, and equivalent rating guides ones it would depend about "the Touhou refefences and depictions, about the Usage& Drinking of Alchohol Smoking, degrees about their occasionality"...
... Strictly Rating. Guides & Tags thy would vary between"E(all ages and completely family friendly) E10+(mature small kids and with partial supervision by mature&responsible 18+/adults) T(maturie teenagers without supervision but not allowed beloe)...
In practice and in reality and with wieving analyses?Mostly E7+, partly E10+, minor T ;. the E and E10+ proportions may and have varied but" the T is Stable as a Minor one".