In Bali it's very easy to get around and see the entire place via a driver. Therefore I'd stay in Seminyak especially with kids. It's geared up for tourists and has a great beach and some really good hotels. (We stayed in a small one called room and Vespa but it was only a few rooms).
Ubud was a bit rough round the edges for me and I got really ill. Candidasa was lovely but very quiet- we did get the boat over to gilli trawangan though which I'd awesome but wouldn'treccomend the boat trip with kids.
Therefore seminyak is a good base with good facilities- enjoy ￼
Hi We've been to a Bali several times with our children and have stayed at the Komaneka Bisma and Monkey Forest in Ubud. Bisma is our favourite. Wonderful hospitality. In Sanur we have stayed at pondok Ayu, which is a very small boutique hotel, very cheap and impeccable service. A driver is included for local travel.