This happened to my daughter last year!
We got a product at out local medical supply company and it worked great.
I just got the box out of the linen closet to copy everything down.
It is called:
Seal-Tight
Cast and Bandage Protector
by Brown Medical Industries
www.brownmed.com
1 800 843-4395
we bought # 20201 (pediatric Medium arm. She was a good sized 8 yr. old at the time and there was plenty of growing room in it. it went above her elbow.
to describe it:
It is light a big thick vinyl mitten with a hard plastic entry hole up at the upper end. Inside this hole is a ring of very firm stretchy rubber. Water cannot get in it. Believe me. It is tight when on. The person at the med. sup. place told me to only leave it on for up to 1/2 an hour at a time.
It is very durable. We used ours for every bath and some swimming too and it doesn't look as if it has even been used. It says on the box that it is non- latex.
I kept it in case anyone else in the family breaks their arm, or if one of the kids friends do and need it for this summer at the neighborhood pool.
I even kept the reciept. It was only 21.95. not too bad I think.
I met a lady at the store the other day who told me that her grandson is in a cast and his mom uses that new "press and seal "plastic wrap to protect his from getting just a little bit wet. This might be a good tip for the wet rides! She just wraps it all around and presses it in place. A roll of that sure wouldn't take up a lot of space in your suitcase!
In any case I hope he is feeling better soon, the first 4 or 5 days is when the pain is the worst and then it doesn't hurt anymore and relax, you are still going to have a great time!
Once you get there, you'll be amazed at how many kids you'll see in casts!!! Take lots of sharpies, Have the characters sign it!!!