The offer sees kids get a free main, snack and drink - worth £3.95 - when an adult spends £5 in an M&S cafe. Kids also entitled to a free piece of fruit with any cafe transaction.
The deal is available in more than 340 of the supermarket’s cafes across the UK.
It comes after Tesco announcemed it is also bringing back its "kids eat free" scheme across its cafes over the October school break.
How long will the deal last?
“Kids eat for free” will run from 17 October until 28 October in England and Scotland. In Wales and Northern Ireland, it will run from 31 October to 4 November.
The free food is from the Kids’ Munch Menu, with hot mains including pancakes, jacket potato, pizza, cheese and tomato pasta and toasties.
Sharry Cramond, marketing and hospitality director at M&S said: “We know customers are feeling the pinch at the moment so we’ve worked really hard to make sure we’re not only offering families a great value and welcoming meal in our cafes over the half term holidays, but a completely delicious one too, even for the fussiest of little eaters.
“Our kids menu is all freshly made with the best quality M&S ingredients, from vitamin-D enriched bread to British outdoor bred pork sausages.
“After all this is not just any free kids’ meal, this is an M&S free kids’ meal. We can’t wait to hear what they think.”
Are other supermarkets offering a deal?
Tesco announced it is also bringing back its "kids eat free" scheme across its cafes over the October half-term, after first introducing the initiative in the summer.
Parents can claim one free kids’ meal worth up to £3.25 when they spend at least 60p. However, you must be a Clubcard holder to be able to take part in the scheme.
The freebie runs on weekdays from 17 to 28 October in England, Scotland and Northern Ireland in 311 Tesco cafes.
Asda has also announced a new £1 cafe deal for struggling pensioners this winter. The "winter warmer" deal consists of soup, roll and unlimited tea or coffee for just £1 for all customers over the age of 60.
The offer will be available across all 205 of its cafes and will run every day through November and December.