(2-part post):
People who've been convicted of a sexual offences are generally free to go where they like, and associate with whom they like, unless they've been released from prison and are still 'on licence'. After 9 years, unless the offence was particularly serious, this is extremely unlikely.
Some offenders are made the subject of a Sex offender's Order which would make it an offence for them, say, to have 'unsupervised access' to a child under 16 years of age. These orders can be imposed both on offenders who are imprisoned and on those who receive non-custodial sentences. However, these orders normally operate for a fixed period of time. Even if such an order was imposed upon the person you refer to, it's likely that it will now have expired.
So, it's unlikely that the person will be committing any criminal offence simply by dating someone with a young child.
People convicted of sexual offences will be placed upon the sex offenders' register. This doesn't prevent the offender from associating with any person but, if the order was still in place, the offender would have to notify the police if he moved in with the woman (or, indeed, if he stayed at her house for 7 or more days in any one year period). Once again, though, it's likely that any order placing the person on the Sex Offenders' Register would have expired by now. (However, for a serious offence involving a lengthy custodial sentence, the registration might still be in place).