Does forgetting the supplication for intercourse ("O Allah, distance Satan from us and distance Satan from what You have provided us with") result in the child being bad or disobedient?

There is no need to worry; this supplication is recommendable, not obligatory, and omitting it does not mean that the child will be disobedient or ill-mannered. There are other reasons for a child's blessing and righteousness, including supplicating for their guidance and well-being, in accordance with the Almighty's saying: "And those who say, 'Our Lord, grant us from among our wives and offspring comfort to our eyes and make us leaders for the righteous.'" Also, good upbringing, discipline, and nurturing them upon virtuous morals and correct beliefs, in compliance with the Almighty's saying: "O you who have believed, protect yourselves and your families from a Fire." A Muslim should rely on Allah in bringing good and repelling evil.