Very used to doing this, and it is worth googling ideas. I think your main decisions are:
Is the jacket to be relegated to 'messing about' - in which case a zig-zag, strengthened by tape is best.
Does he want to make it as good as possible, for show, in which case I would use a repair that sews up the pocket - a shame not to have a useful pocket - but could still look smart. Sewing by hand I would do a sort of darning / running stitch. Sometimes, if doing away with the pocket, you can use thread from the pocket to 'invisibly darn'.
Could you add a motif, contrasting tape or similar to make a feature - and jazz up other bits of the jacket so it looks intentional? There are loads of motifs on haby sites.
I have once, taken a contrasting piece of fabric and made 2 new 'patch pockets - but probably not if you're working by hand.
Hope that helps!