Decorating an Antique Rocking Horse

You could dress it up for each season or each month like those geese you see outside, rain jackets, santa hat, bows for mane in different ribbons

Sand and stain if it needs it. Or, you could paint it like a carousel horse, or put a cowboy bandanna on it, or a superhero cape, or whatever he is into. You might let him help you dress it up to suit his taste.

Try restaining it if wooden.
Get some rope and tie around neck and make tail.
Also you could get some eyes in craft dept. and clue on.