What do you recommend to the younger or ambitious devs who want to grow in their career -- do you send them to training or let them have a side project of some

What do you recommend to the younger or ambitious devs who want to grow in their career -- do you send them to training or let them have a side project of some kind so that they still have a somewhat valuable resume, or is it more a question of trying not to get junior devs (who need the resume building badly) in the first place? I'm curious because I work at a big company but not in a maintenance or operational role so I'm not sure what an "ideal" resume or career track looks like for such people.