My 2 year old mistakenly drank after a friend of the family who is (male to female transitioned and unknown status) should i be worried of possible stds/hiv transmission to so worried?

STDs are called that for a reason. Sexual activity creates the environment where infectious fluids are exchanged & the germs pass in them. Most (like HIV) die when exposed to the outside world and these don't pass like you would see strep or staph transfer. Risk from a cup as described is negligible. I wouldn't spend ANY more time worrying about it.