The former Real Madrid captain's children, aged 12 and 10 respectively, have been part of the club's youth system since the prebenjamín age group. Their departure has been communicated internally, with the family now preparing to find a new environment for the boys to continue playing.
Martín, the older of the two, has been playing for Infantil B, while Lucas has been part of Alevín A, where matches are still played in a seven-a-side format.
Both have followed their father into goalkeeping, the position in which Casillas became one of the most decorated players in Real Madrid's history. He won three Champions League titles with the club and made 725 appearances for the first team.
The decision to leave is understood to have come from the boys themselves after discussions with their family. Their time at Valdebebas has included opportunities to represent the club in youth competitions, but they are now ready for a change of surroundings.
Lucas recently attracted attention after a series of saves in a penalty shootout against Barcelona went viral. Martín had also impressed at the Under-12 World Cup tournament in Brunete in March.
However, competition for places has increased within the academy. Martín had lost some prominence in his age group, while Lucas was not included in Real Madrid's squad for the recent Futures tournament in Orlando.
Those developments formed part of the wider picture as the family considered the next step, although the decision has been presented as one driven by the boys' wishes rather than a dispute with the club.
Casillas has previously spoken about the challenges his children could face because of their father's reputation. He believes having a famous parent can bring additional scrutiny and make it harder for young players to establish their own identities.
"I think they have it much more difficult than us, especially if your father has been someone recognised in the world of football, because in the end they will always be comparing you," he said in an interview with Santi Cañizares.
The former goalkeeper has also insisted he does not want to pressure his children into following his career.
"I'm not like my father when I was little. Since I liked football, we were playing all day. He would kick the ball at me and take me to school to play and I loved it, but I, in that sense, am not a father who encourages his children to play football."
Martín and Lucas will now look for another club where they can continue developing as goalkeepers, bringing their spell in the Real Madrid academy to an end.