Is it safe to give my 5 year old albuterol from breathing treatment machine. It was prescribed to my 11 month old for bronchitis?

Only if doctor says. If your 5 year old has been diagnosed with asthma previously and is now having the same symptoms, you can give it, but call your pediatricians and let them know you're doing so. If your 5 year old has never had this problem before, it's best to have him/her seen by the pediatrician to get a correct diagnosis and see what the best treatment is for that diagnosis, since it may not be asthma.
If he needs it. It is safe if there is a real need. You could do about 2.5mg.