Apart from Ibiza Town, which is worth a good day spent there (and if possible an evening & night - but with kids may be difficult) the other main things to get to see are the other resorts to get a feel of what is on offer.

This is something I did for a couple of visits - hired a car, got round to see as much of the Island as possible (not too difficult) made a mental note of some of the places and Hotels so that when I got home and started to plan again I had some idea of what to expect.

Some of the other resorts worth a look
Portinax
Peurto San Miguel
Calla LLonga
San Antonio (either on the Bay side away from the main town or Cala Gracio in the other direction)
Playa den Bossa

From your other post - Es Cana is nearest to Santa Eulalia - the Hippy Market is there every Wednesday but be warned it gets very busy.
Can't help with taxi fares, but the alternative is bus or ferry.
Santa Eulalia itself has a fine beach with plenty of shops and eating places in and around the town. Es Cana is still worth a visit to though

Hope this helps

The caves are worth a visit, you are taken round by a guide who gives you the history in multiple languages including english and they have a waterfall with a light show. There are plently of leaflets around the island (including hotel entrances)

The caves are called San marco (I think) and are close to Puerto San Miguel. The view from the path as you walk down to the cave entrance is really something (Given that the path is a platform built into the cliff high above the sea)!

I agree that a visit to the old town (Vila D'Alt) is a must and a return on the night to cruise around the harbour area is another.

cala D'Hort is a quiet spot (except on Sundays).

The best way to get around is to hire a car. There are buses but they tend to use Ibiza town as a hub and so all journeys will involve going into and then out of Ibiza town.

Portinatx is nice and there are many tiny bays and inlets.

cala San Vincente is quiet athough the sand is a little coarse and so not good for sand castles.

you must visit the hippy market while you are there its wicked

fizz xxx

You may find these websites useful as well as Holidaytruths of course...

http://www.hippymarket.com/ For all the info on the Hippy Market (in english, spanish and german)

and

http://www.virtualtourist.com/travel/Europe/Spain/Balearic_Islands/Ibiza-265785/Things_To_Do-Ibiza-Hippy_Market-BR-1.html VirtualTourists pages about Ibiza, which if you scroll down to the bottom gives loads of really good tips and places to see in Ibiza... just discovered this myself actually so I am off to read it as well!

Hope you and your family have a fantasic holiday on Ibiza!

If you like to drive around on holiday, I recommend getting a car for 3 days and just exploring. The interior of the island can be stunning (red soil, olive/fig/almond trees, etc.) A few nice places for a pit stop are Santa Gertrudis (central, not too far from Sta Eulalia). There's a great bar called Bar Costa - go in and check out the artwork and hams hanging all over the ceiling. Also try the bocadillas (sandwiches).

Santa Anita also has a few nice bars/places to eat. Bar Anita is popular as the old "hippy" hangout, but if that's full then we found a lovely place just round the corner - great salads for lunch.

Also, check out some of the Ibiza websites which mention all the different beaches, and find a nice beach for a day. There are some stunning little coves, which you need a car to get to. Be warned that some of the roads are a bit hairy! Cala D'Hort is lovely, and the drive over the mountain from St Josep is also very scenic. You'll see amazing views of San An.

Oops, just noticed you asked about day trips for a family... I would still recommend all of the above, but depends what your children like to do/see and how old they are. Driving about may not suit them, although most places only take an hour or so to get to.

Apparently they filmed some of South Pacific on Ibiza. Portinatx was used in one scene and the big island off the beach at Cala d'hort was used as bali hi.

Es Vedra is the island... one of the reasons that Cala D'Hort is a favourite beach of ours

Found this great link.. check out the "Beaches" section.....

http://www.ibizaholidays.com/Es%20Vedra/