It's his right hind leg Diane, BUT watching him run, play and buck (plus rearing up at his Momma!), he is dealing with life just like any other foal.
Sweety is extremely protective isn't she - to be expected, as I always feel mares know when something is not quite right with their babies, plus she had to put up with the vet 'doing' things to her baby more or less as soon as he was born, and this can affect some mares. I would not worry her any more at the moment Jenny, trying to get videos for us because I dont like to see Sweety push little Beau around when trying to keep him away from camera close-ups, he doesn't need to be pushed to use his legs more than he would be doing naturally - anyway the odd picture from now on will keep us all happy!
I am shocked at the cost of surgery - it would be way out of the pockets of most of us! But I agree with the others, you have a happy little foal and a happy mare, so I would just leave them be to enjoy life for now. I do think that you will still have to keep him separated from your other foals as he is not ready yet to start the rough and tumble, play fighting that goes on, but other than this, I wouldn't change anything.
Well I WOULD change one thing.......you seriously have to get that headcollar OFF Sweety - if Beau starts rearing up at her head (especially when her head is down eating) there is a 90% chance that he will slip a front leg through her noseband, with really tragic consequences.
I'm sure that if Sweety is not easy to catch, you can entice her into the barn/stable with a bowl of food and then put the headcollar on when you want to handle her, but remove is as soon as you have finished? Sorry to keep on about this, but just thinking of little Beau (plus the thousands of other 'accidents' that have happened to horses of all sizes through just being left with headcollars on when turned out.)
But aside from all that, I'm 100% behind you and am saying daily prayers for you and little Beau. Sending huge ((((HUGS)))) too - chin up, where there is life there is hope!