The fine served to Erin Fitzpatrick and her family was quashed.
Family-run business The Dutch Bike Shop, based in Goatstown, County Dublin was served with the fine after daughter Erin offered to wash bikes.
Mother to Erin, Astrid Fitzpatrick arrived into work on Wednesday to find a fine in the post from the local Dún Laoghaire-Rathdown County Council.
The posters, put up by Erin on June 9, asked for €3 for a bicycle wash and €4 for a wash and polish but it wasn't until June 13 that the owners of the bike shop realised the posters were a breach.
Mrs Fitzpatrick said the children made little to no money on the day: "Erin made just over a tenner on the day, and we get hit with a €150 bill".
"I am not going to get cross with the kids, at least hey are being inventive, doing something useful instead of staring at a screen at home. They have to keep coming more [to the shop] often over the summer, and I don’t want them to get bored. Rather have them excited for earning some ice cream money," she added.
The Dutch Bike Shop said they were "feeling annoyed" by the fine and couldn't understand how the person responsible for sending the fine didn't see it was a "kid's sign".
Following outrage over the €150 fine for Erin and her 8-year-old sister Roisin, putting up the posters, Minister for Transport Shane Ross wrote a draft letter for the family and asked waste management services in the area to quash the fine.
Dun Laoighre-Rathdown council said in a statement: "At the time the fine was issued on Sunday morning, the shop was closed and so the litter warden could not speak to the owners about the sign.
"An appeal has been lodged, the circumstances explained and the fine will be written off."