One thing that helps me is to remember that strong and overwhelming emotions are a physiological response to a threat to life. Why does it help to remember this? Because when it happens in response to a fairly typical life event where there is no threat to life (say a conflict with another person) then it is a trauma response from the past.
If it is a fairly normal everyday incident and there is no immediate threat to life and you are flooded with overwhelming emotions then your experience is due to a physiological trauma response from the past.
Once you are able to connect the current feelings with the awareness that it is an activated response from the past you can begin to apply grounding strategies to calm the trauma response. Use strategies to connect to the physiological experience of the present moment. Multi-sensory awareness of the immediate surroundings works best for me. And then verbal comfort - There is no threat, we are well, we are safe, we are right here in this room in 2019, here and now we are perfectly safe etc.
Once grounded THEN you can begin to ask parts about what was happening for them, why the current event triggered that response etc. Grounding and connecting to the present, and calming the overaroused amygdala comes first.

If you are unsuccessful talking through to the younger parts when you are triggered you could try thinking of it all in terms of physiology. What IS happening when triggered IS that the amygdala is activated the prefrontal cortex is essentially hijacked. once the amygdala is calmed by grounding techniques you can then begin to support the younger parts. It always works better when they are not in an activated state.