Parents may want to be careful about letting their children eat too many chocolate rabbits this Easter weekend, as a health watchdog group has released a list of popular chocolate brands that it says contains unsafe amounts of heavy metals.

The San Francisco-based advocacy group As You Sow said that heavy metals like lead and cadmium can stay in a person's system for years and are extremely dangerous for children.

Cadmium is known to cause harm to the kidney, liver and bones through chronic exposure. As You Sow CEO Andrew Behar noted that lead can cause a loss of IQ as well as neurological damage, adding that there is no safe limit of lead for children.

The group tested around 50 types of chocolate and said that 35 of them tested positive for lead or cadmium - or both. The levels were found to be above California's limits, which are much stricter than federal guidelines.

"We assumed that companies were testing their products before they put them on the market, but they're not," Behar said.

Popular brands that were mentioned on the list include Hershey's, Chocolove, Earth Circle Foods, Lake Champlain Chocolates, Theo Chocolate and See's Candies. Others include Dove, Trader Joe's, Lindt, Ghirardelli, Cadbury, Godiva, Mars and Whole Foods.

Lead was found in 17 of the tested chocolates, including Cadbury's Royal Dark Mini Eggs and Royal Dark Chocolate Bar, Godiva's 72 percent and 50 percent cacao dark chocolate and Hershey's Special Dark.

Cadmium was found in seven of the chocolates, which included Ghirardelli's Intense Dark Twilight Delight and Dove's Dark Chocolate.

As You Sow said that it approached all of the companies on the list about the results, adding that only two of them have asked to work with the group to solve the issue, while the others claimed that the products are safe to eat and the metals are from naturally occurring sources.

"Some minerals - like cadmium and lead - are found naturally in many foods, including seafood, peanuts, potatoes, grains, leafy vegetables and - sometimes - cocoa beans," the National Confectioners Association said. "Cocoa-based foods are consumed in small amounts and are not a major source of these minerals in the diet."