Especially in a nursery, I would enclose by boxing in from floor to ceiling and add decorative trim. In case access is ever required, front could be a hinged panel.

I would not even make it anything to draw your eye so just box it in with drywall and paint the same as the walls what is there still baseboard heat if you have new HVAC

Does this go horizontally above the floor as well?

Thanks for the ideas. The baseboard heat is still there for super cold days unfortunately. we may remove if the new system is sufficient.

If it goes horizontally you will probably need to reroute that older baseboard radiator and fashion some sort of window seat type thing to conceal that, it has to be big enough to not compress that tube.