Lynsey Calvert said staff at the Movie Starr cinema in Canvey, Essex, insisted she pay £3 for little Samuel, even though he is too small to sit.
"I was absolutely outraged," she said.
But Lynsey's anger has provoked a tirade of criticism from other film-goers who said the cinema was no place for a baby.
One said: "The sound of hearing a baby cry in the cinema when you are paying to watch a film makes you want a refund. It's worse than the people opening crisp packets. She should be ashamed of herself!"
Lynsey, 37, of Benfleet, Essex, had to cough up the same charge for herself and her two other sons Oscar, five, and Max, two, to see new flick Mirror Mirror.
She said: "Samuel is too young to even keep his head up to watch the film and sat in a sling the whole time. "I just feel like they have taken advantage because I could hardly turn round and say no, and disappoint my two other children."
The furore has echoes of former Apprentice contestant Katie Hopkins' call for "squawking breastfeeding babies" to be banned from events at the forthcoming Olympics.
Katie defended 2012 chiefs who had declared that babies born AFTER their parents bought tickets for the Games would have to have a ticket to get in.
Lynsey said she was shocked and surprised at having to pay as cinema giants Odeon and Empire, who have screens in Southend and Basildon, don't charge for small babies.
Entertaining three children for two weeks over the Easter holidays can be hard and very expensive, so you need to try and keep everything as cheap as possible," she added.
"The reason we come to this cinema is because travelling to the bigger ones costs too much in fuel.
"I am all for championing smaller businesses, but I am seriously thinking twice about coming here again. You would think they would have more flexibility over things like this."
Movie Starr owner Shane Parkin said: "Legally everyone has to be issued a ticket due to fire regulations. If a fire were to happen they would need to know how many people are in the premises.
"So regardless of age, regardless of money, everyone has to be issued a ticket. We are deeply sorry that the customer has complained and I apologise for not being available to attend to the matter personally."
But Lynsey has been attacked by other cinema-goers. One critic wrote on the Sun's website: "A 10 week old baby should not be in the cinema. The lights and sound are overwhelming and I would hazard a guess that it damages their eardrums. What a stupid thing to do!"
What do you think? Have you taken your baby to the cinema?
Do you go to special mother and baby cinema screenings?