MOSCOW — The 11-year-old boy's Moscow bank savings card has a picture of a cute cartoon dog with its tongue hanging out, dark glasses and a yellow hat. He saved more than $400.

But when Zakhar Navalny checked Monday, it was all gone. His family was about to find out that when it comes to opponents of Russian President Vladimir Putin, children are fair game.

Alexei Navalny — Zakhar’s father and Russia’s main opposition leader — and his Anti-Corruption Foundation are under attack by Russian authorities, which last year designated the group a foreign agent and accused it of money laundering.

“Someone took 30,000 rubles that I saved up from my account,” Zakhar messaged his father Monday. There was a similar message from his wife, Yulia.

And his daughter.

And his mother.

Navalny announced Tuesday that authorities not only seized the contents of his bank account, but also those of his son, wife and daughter, Daria, who is studying at Stanford and found out about the problem when she tried to buy breakfast in a cafe. Navalny described those accounts as having been emptied and frozen.

In addition, he said, his parents were informed that their account was blocked, two days before their pensions were due.

“This is very unpleasant, frankly speaking,” Navalny posted on his website Tuesday. “My parents are elderly people, pensioners. Like anyone, they might get sick. They need to buy medicine and so on, and now what? How shall we pay for housing and utilities?”

Navalny says the money-laundering case — which asserts that his foundation survives on “illegally laundered funds of illegal origin” — has no basis. The foundation subsists on donations from supporters, he wrote.

“Putin is getting scared and vindictive. He’s just frozen all the bank accounts of Alexey Navalny, his elderly parents and even his children,” tweeted Bill Browder, a prominent Putin critic. Browder spearheaded a campaign that led to the 2012 Magnitsky Act, U.S. legislation that sanctions foreign officials involved in human rights abuses. It is named after Sergei Magnitsky, a Russian tax auditor who died in prison after he was jailed for exposing Russian corruption.

On Monday, Navalny was informed that billionaire Oleg Deripaska, who has strong ties to the Kremlin, was suing him for unknown reasons.

Navalny has been barred from running for election and has frequently been jailed and harassed. The latest actions against the family’s bank accounts came on the third anniversary of a scathing YouTube video by Navalny and his team that exposed the wealth of Dmitry Medvedev, then Russia’s prime minister. The video showed drone footage of a palatial residence outside Moscow with towers, glass houses, sweeping lawns, a pool, a garage, a small forest, a lake and even a house for ducks.

The 49-minute video, viewed more than 33 million times, helped precipitate a sharp decline in Medvedev’s popularity and that of his government.

Putin dismissed Medvedev and the government in January and named Mikhail Mishustin as prime minister — who was soon fingered in a new YouTube video by Navalny. It alleged that Mishu­stin’s family owned property worth about $50 million, even though the he has been a civil servant for 22 years.

The director of the Anti-Corruption Foundation, Ivan ­Zhdanov, also saw his accounts and those of family members frozen Monday. Zhdanov has been charged with failing to comply with a court order to take down the Medvedev video.

In the fall, masked police raided Navalny’s offices in 30 locations across Russia. The Investigative Committee, a federal unit that reports to Putin, accused employees of the Anti-Corruption Foundation in August of obtaining more than a billion rubles (nearly $16 million) in funding by criminal means, a figure later revised to 75 million rubles, or nearly $1.2 million. On Monday, authorities debited 75 million rubles from Navalny’s account, noting that this was the result of a criminal case. ­Zhdanov’s account was also debited.

The action comes as Putin faces a crucial moment, with plans for a vote on constitutional changes that analysts see as opening a way for him to retain power after his presidential term ends in 2024. Authorities are sensitive to criticism over the constitutional amendments, apparently fearful that if voter turnout falls short, it could undermine the plebiscite’s legitimacy.

Putin recently submitted his proposed constitutional amendments to the State Duma, or lower house of parliament. They include conservative measures designed to appeal to traditionalists: references to Russians’ faith in God, to Russian unity and to the Russian values passed down through generations from forebears, as well as an amendment stating that marriage exists only between a man and a woman.

The amendments will be packaged in one bill, with Russians able to vote yes or no in a nationwide plebiscite next month.

Another element includes a bar on ceding any Russian territory, raising doubts on whether disputed lands including Crimea and the Kuril Islands, known in Japan as the Northern Territories, could ever be returned to Ukraine and Japan respectively. The amendments would also give Russian law precedence over international law.

They would enshrine the constitutional status of the State Council, a body that analysts believe could be used as a vehicle for Putin to wield power after 2024.

“Putin is nervous again. He is worrying and stamping his feet,” Navalny posted in a blog on his website Tuesday. “People are laughing at his amendments. Nobody is even angry any more.”

The opposition leader continued: “They can add whatever they like to the constitution. It is clear that with that kind of voting procedure, you might as well stop discussing amendments. The turnout and the results will be falsified 100%. They can add either God or the devil or nuclear forces or even victory in all coming Eurovision contests.”