I think you will find some very helpful information on this website.
Bali for families
Hope the link works, otherwise just google it.
As far as accommodation is concerned and depending on what you find on the Bali for Families website you might also like to look at Suri Wathi, a losmen in Jl. Menuh, Legian or Garden View Hotel/Cottages in Jl Padma Utara, Legian. Both places are budget priced, well located and comfortable. You could google both of these places for details.
For your first time in Bali, organized tours of ancient sites and temples would be very worthwhile and include trips to the Bird Park and the Reptile Park, the Bali Zoo and the Elephant Park, the children will love these. Sometimes if you package these "Park" visits you will get a better deal.
The Elephant Park is north of Ubud so that would be good to think about when staying in that area. Tegal Sari is located at Pengosokan, a lovely area just out of the immediate Ubud village and the walking is lovely around here. There is accommodation everywhere so no danger of being without a place to stay.
I must rush off, but will reply further over the next few days.
Catherine