Derbyshire is great, lots of greenery, wildlife etc, but there are small pockets of deprivation with the usual problems that brings e.g. bits of Alfreton, some former mining towns, inner city Derby etc.
Wirksworth is considered quite desirable, lots of 'arty' people, coffee shops etc, but again there are a few dodgy places, best to visit for a few days if possible to get an idea.
The drugs thing is under control and the local police are very good and very tough, the 'county lines' bs from Derby/Sheff/Manc have tried to get a foothold here but have mostly been seen off pretty effectively, which is brilliant news.
Kids can get weed easily enough here if they know where to go, but equally they can easily avoid it if they wish. Luckily, for harder stuff you'd really have to go to a big city, and long may it remain so.
People here are warm but honest, and the culture is quite traditional. I'd say it's one of the safest places in England to bring up kids, hope that helps.