Sandra Bullock's child has ''a really tender heart.''

The 'Gravity' actress, who has adopted five-year-old son Louis, admits she spent much of Mother's Day in ''happy tears'' recently after he surprised her by performing a special song.

Asked how they celebrated the occasion, which took place in the US on May 10, the 50-year-old star said: ''Cried a lot. It was all happy tears. It was happy tears. It was so much. I just cry at anything now. I feel like, I mean I didn't have him that way [give birth to him], but I feel like hormonally...''

Louis performed his own version of 'Bingo Was His Name-O' about the 'Minions' star.

She told 'The Ellen DeGeneres Show': ''He said, 'I wrote you a song,' and I didn't have the heart to tell him he plagiarised. [He sang,] 'There was a mom l love so much and Sandy was her name-o...' And then he played the harmonica in between and then he just kept looking at me. I just [cried]. It's too much. He's all boy with a really tender heart.''

The Oscar winner, who adopted Louis in 2010 shortly after she split from ex-husband Jesse James, previously admitted her family isn't what she expected.

She said: ''There are so many variations of families out there that are perfect. My family looks nothing like I ever imagined it would. It's better than I ever imagined.''