From NetFlix:

Will Lightman (Hugh Grant) is a rich, hip, irresponsible
Londoner who, in search of available women, invents an
imaginary son and starts attending single-parent meetings —
confident in both parties’ inability to make a commitment.
But when Will meets Marcus, the troubled 12-year-old son of
Fiona (Toni Collette), a quirky and unexpected friendship
develops as both Will and Marcus help each other grow up.

Another suggestion from Kate and Nigel, “About A Boy” is a feel-good lightweight
film that avoids being maudlin. Hugh Grant does a nice job, as do the kids in the
movie. Possibly not for children due to its explicit sexual references. Just a bit of fun.