just a simple question about balloons  

No, I don't think it would have been inappropriate at all but everyone has their own opinions I guess. I can understand your father not wanting to focus on your mother being in the hospital on her birthday but the fact is that she is in the hospital so a Get Well Soon balloon wouldn't have been out of place. I hope your mom does get well soon.

I think that buying both balloons was a nice idea... but not to be given to her at the same time. Here's my thinking... it was unfortunate that she had to spend her birthday in the hospital but lovely that you threw her a surprise party there. I'm sure the objective was to make her happy, to let her enjoy her special day, no matter where her surroundings, and to let her spend time with those she loves. She knows full well about her illness and knew where she was for the party, so I don't really believe that a Get Well Soon balloon was necessary at that time. She didn't need to be reminded. It was right to let her celebrate her birthday as JUST her birthday :) The other balloon could have been given before or after the birthday party. I would not have given it during the party.

I hope the party was nice for your mother and I hope she is well soon :D

I don't think she needed a balloon to remind her that she's sick! She's in a hospital for crying out loud! I'm sure she's reminded of it every minute! I would have gone ahead and gotten her both! Because you do want to wish her a happy birthday, and you also want her to get well soon! If I were in your mother's position, I would have been happy to get the balloons and wouldn't have thought it was inappropriate or felt bad that I'd been reminded I'm sick on my birthday. I just would have greatly appreciated the sentiment.

You can put the "Happy Birthday" thing on the balloon but I would suggest you can just put the "get well soon thing" in words. Would you want to see the balloon later on and see "get well soon" printed on it. It would we more appropriate to just put Happy Birthday on the balloon.

I don't think it would be inappropriate. You could even have bought her the get well balloon and given it to her the next day or some time after her birthday. I think she would have enjoyed the balloons no matter what.

i think that you should just get the balloon with the Happy Birthday on it. you're father is right, your mom should not think for a while that she is in the hospital and that she has an illness just for that day.
i am sure that your mom is very proud on you for being so kind.
wish me good luck to your mom.

Sure, why not? I'd think it was a nice gesture.