Sammie Welch was travelling with her three-year-old son on a busy First Great Western train from Birmingham to Plymouth on Thursday evening when a man handed her a note as he got off the station in Bristol.
The mystery passenger, who signed the message “Man on train at table with glasses and hat”, also left the woman a £5 note to buy herself a drink after apparently being impressed with the way she spoke to her son.
The note, in capital letters, read: “Have a drink on me. You are a credit to your generation, polite and teaching the little boy good manners.
“PS I have a daughter your age, someone did the same for her once. Hope when she has children she is as good a mother as you.
“Have a lovely evening.”
Ms Welch, 23, who is originally from Crewe but now living in Plymouth, said she “wanted to cry” at the anonymous benefactor’s generosity.
She said: “I never had the chance to thank him as he got off and I couldn’t move due to my son being asleep on me and a man sat next to me.
“I would love to have the opportunity to thank this man personally. He may not have Facebook but please please share this! I want to thank him for his kindness!”
She has appealed on Facebook for people to get in touch with the man.