Probably the safest field to get into would be everyday things, especially plumbing. There's no automating that, pipes will always break and new (and old) buildings will always need to manage complex plumbing systems.
I wouldn't be surprised if some black swan breakthrough in automated assembly/modularization/mobility of housing in less than 30 years halves the availability of manual plumbing work so that when your children just get 1 to 10 years into that career there is a sudden plummet of pay, possibly combined with an influx of workers coming in from previously wrecked markets.