W3W combined with a text message is a lot more kid friendly in my opinion which is why I've done it.
Plus I've gone through the W3W strings that are near enough my house to pick ones that are easier to not mis-spell, many of the words they use would be tricky for a young un. Any emergency service not up to speed in the UK with W3W would hardly be put out by using it, or converting it.
I have read the perfectly understandable criticism of it, the fact that the "unique" identifiers are only unique within the 32 (?) languages they use, and OS is of course awesome. DMMSS.SS or DM.MMM or D.DDDD can be confused too, one mis-keyed grid reference for someone not paying attention, etc.
Just one idea for one scenario for my son.