Some of the most popular kids cereals are being voluntarily recalled.

Kellogg Company has announced a recall of about 28 million boxes of Apple Jacks, Corn Pops, Fruit Loops and Honey Smacks cereals because of an unusual smell and flavor from the packages’ liners.

The company said about 20 people have complained about feeling ill and  five had become sick with nausea and vomiting.

According to a Kellogg spokesperson, consumers said the cereal smelled or tasted waxy or soapy and some said it tasted stale.

Kellogg is trying to figure out the substance that may be causing the problem and is offering consumers full refunds.

The cereals in question were in stores beginning in March and include the letters “KN” after the use-by date.

If you are concerned about the recall or want a refund, you can contact the Kellogg Consumer Response Center 1-888-801-4163.