Air carrier Captain reported a CFTT event during approach to DSM airport resulting in a go-around.

Narrative

We were on a visual approach in DSM to runway 13. ATC gave us the visual with a 5 mile left base between 2500 MSL to 3000 MSL in clear VMC. We backed up the approach with the ILS 13 for guidance. We were stable and looking good to continue. The FO who was pilot flying didn't seem to mind the vector and seemed confident. For our base to final turn it got busy; configuring the plane; getting a landing clearance; and capturing the glidepath down. The FO bugged roughly 1500 and then 1000 in the altitude selector and selected vertical speed mode with about a 1.5 descent rate. As I was processing why the altitude was selected that altitude I said 1300 was the MDA (which is charted as 1240 MSL in LOC 13) I then noticed the descent rate and altitude. I told him to shallow the descent. Tower called saying we were 'getting a little low' and I realized this approach could not be continued and I called for a go-around. When the go-around was initiated we were between 600-700 RA; about 1500 MSL on roughly a 4 mile final. The second approach was normal without incident.Cause: I am a new captain who has flown with mostly fairly experienced FO's. I was caught off guard when the FO made this mistake. Things happened very quickly and I should have reacted quicker to his automation choices and possibly encouraged him to fly the approach autopilot off. In retrospect I should have kept a more keen eye on him and asked if he was comfortable with the vectors ATC gave us. There was a lag with correcting the airplane's path and go-around procedure; and I probably should have taken over to ensure correction. I should have also been more acutely aware of altitude.Suggestions: In initial training it would be nice to have FOs experience a 5 mile visual approach in the sims; since it's somewhat common in outstations and may not happen on OE. I know that's not typically in the syllabus during training. I'm sure this is a common mistake to make since inexperienced FOs are not comfortable with the speed of the aircraft yet. As far as captains; an awareness to keep sharp on situational awareness with the automation during high workload moments; and to not become complacent with a confident FO.