Yes, Ravi's mother will most likely get to know about what happened. When she asked what they did that day, Grandpa coolly replied that Ravi had "disappeared instead of staying at home" to look after him, which directly reveals that Ravi did not fulfill his responsibility.

Furthermore, Grandpa had a gift-wrapped parcel for Ravi, which indicates he had gone out and purchased something. This would naturally raise questions from Ravi's mother about how Grandpa went out alone when she had strictly instructed Ravi not to let him go out on his own. Ravi's confused and embarrassed reaction would also make his mother suspicious, making it difficult for him to hide the truth.