Hi, first of all id like to say you will have a fantastic time, and so will your 8year old.
Are you going to North or South Goa?
Plugs - we buy ours from the nearest shop once we get there. They cost around 1pound, and most shops sell them.
Last year we got a plug from the electrical shop on the main calangute road, and we still have it now. But any local shop will sell them, not just electrical shops.
Cash/travellers cheques - we take the bulk of our money in sterling travellers cheques. Yes you will be paying a bit more to exchange them, but its the safety that counts.
We always take some pounds though.
change the money at local shops and not in your hotel, as you will get a better rate.
Trips - Theres lots of different trips, but i would say avoid going on the crocodile trip.
I went on this trip with my parents when i was a teenager, and we were on a boat from 10am-5pm without any shelter from the sun, needless to say i got sunstroke
Theres a waterfall trip, which i have heard is very good. It is going to be my 7th visit in a couple of weeks and i still havent been to see the waterfalls.
Theres a website called daytrippers, if you google it you will find lots of trips.
Theres shopping in the capital Panjim. Theres Old Goa, which is a nice afternoon out of the sun.
Theres a waterpark in Arpora, which any taxi driver will know. Its not too far from the main stretch of baga and calangute.
What to pack - malaria tablets, first aid kit (plasters, savlon etc) , a torch, basic holiday clothes like shorts, tops.
Dont pack much white clothes as the dust will stain them. Also it is very warm so you wont need warm clothes obviously.