Meta - as Facebook's parent company is now called - said messaging encryption on the apps would now come in 2023.
The process means only the sender and receiver can read messages, but law enforcement or Meta cannot.
However, child protection groups and politicians have warned that it could hamper police investigating child abuse.
The National Society for the Prevention of Cruelty to Children (NSPCC), has claimed that private messaging "is the front line of child sexual abuse".
UK Home Secretary Priti Patel has also criticised the technology, saying earlier this year that it could "severely hamper" law enforcement in pursuing criminal activity, including online child abuse.