We were in Gibralter this August. We did not take an organized tour. Wew were in Spain and parked on the Spain side and walked over the boarder. Once there, instead of a tour we caught a bus to the central part of town (Main street - lots of restaurants and shopping) and then walked to the cable car. It was a pretty good walk, but doable for two adults and a 6 year-old (I carried the 2 year-old). There are some interesting sites along the way. If you are used to walking you won't have any trouble with it.
I am not sure about bus service from the port (I"d guess there is) but imagine you could just catch a taxi. The cable car ride up involved a pretty long wait on line (like 45 mintues). The ride up was fun - good views. Children under 4 or so are free. All all-day pass on the bus was something like .90 euro. I think the cable car for the 4 of us (youngest was free though) was 20 Euro (round trip), and that was one way and did not include some of the other sites.
The kids LOVED the monkeys at the top cable car station. It was the thing they remember the most of our 3 week vacation. Be warned - they do snatch things (don't take any plastic '
Walmart' type shopping bags or food up with you). THere is a little snack bar at the top. You can climb around some of the old battlements and mail a post card. The views are pretty incredible. From the top, if you choose, you can walk down to the other sites that a tour would take you to (St. Michael's Cave, etc.)
Here is a link with tickets and times for the cable cars.
(I can't post the link I don't have enough posts yet...
If you google gibralter cable car you can find a link)
The advantage of the taxi tours is that if you don't like cable cars - you get to skip that fear inducing event. And, you avoid the lines. And instead of walking you will drive to each site.
We needed down time from the day and there were lots of restaurants around the mainstreet area. The town is very pretty and nicely walkable. Outside of the downtown area - closer to the port - there is a McDonalds with a large indoor playscape. I know it is a total cliche of the American tourist - but our kids are little and they were so happy to be at McDonalds and have a chance to run around and get some wiggles out.
Gibralter was really expensive! The offical currency is the Pound, but pretty much every place will talke Euro as well.