Can one keep from spreading MRSA bacteria no matter how careful one is when you share the same shower/bathtub?

Since the MRSA has already cleared up I would be vigilant. As long as you practice good hygiene which is evident in your statement, then I would go and have a good time. As long as the children are healthy, then you shouldn't have any problems being close. I hope that this alleviates your concerns. Have fun and enjoy yourself.