Edinburgh Bus Tours do tours to South Queensferry which includes a cruise of the Forth. They do a 48hr pass that covers all their other tours around Edinburgh as well https://edinburghtour.com/3-bridges-tour/ More on reddit.com

I think the problem is often that knackered old buses with ancient and worn out engines have the tops cut off to make them into tour buses. Electric buses would make much more sense, but also smaller ones. More on reddit.com

Used to like taking the 26 to work along porty when I worked in Musselburgh. Was nice at a certain time of year when the sun was rising over the sea. More on reddit.com

Personally I recommend Camera Obscura as I have a 2 year old who loves it, but it is expensive. The national museum of Scotland is also great for kids and is completely free, you could spend a whole day in there but your food costs for a family could be high so maybe eat elsewhere to save a little cash. Princes Street Gardens West has a nice play park and you're right in the city centre. The museum if childhood is a snore fest for little kids so don't let the name fool you. The castle is good but not so great for younger children in my opinion. Feel free to message me for more input. I've worked in Visitor Services in Edinburgh for 13 years. More on reddit.com