The Kodomo No Omocha OVA is a thirty-minute animation video that was made before the TV series. It covers the first volume of the manga, so it's equivalent to TV episodes 1-6. It relates Sana's troubles with Hayama at school as a result of the "oyakodon baka" situation and culminates when Hayama's dad and sister realize their mistakes thanks to Sana's efforts.

(Source: AniDB)