Cordless shades to start with. As he grows older you can add a simple curtain panel to each side of the two corner windows. Short ones at first and the longer ones if you're still here once he's in junior high school.

Is that the only means of egress? Is the window sized and positioned properly to be able to use the room as a bedroom and god forbid emergency egress if there were a fire?

I would hang a mirror same size to reflect light. up/down (Blinds.com) shades for now, a drape when he is older.

Most (if not all) newer mini-blinds come without cords. One disadvantage is that you must make reaching the blinds easier to raise or lower them -- especially the wider ones if you're going to raise / lower them evenly tend to require using both hands.

Mini blinds often work best if they're installed inside the window frame rather than overlapping it but there doesn't appear to be a left frame for the window(s) ... so ... you could add a 2"x4 trim board above the window(s) and hang the blinds from beneath that board.

Is that two windows or just the one with something else to the left on the other wall?