hi tomcat......take what you need for about 3 days in euros...or as much as you feel safe with.... and the rest in sterling travellers cheques....plenty of places to cash travellers cheques in salou.....you usually only get a good rate here if you get over £500 some say £600....by the time you pay card charges for regularly drawing cash abroad you are no worse off with travellers cheques.....if you get sterling ones you wont loose out if you need cash them when you get back home.....and you cant guarantee what rate to the pound you get if you draw euros from ATM....probably the same rate as changing your sterling travellers cheques for euros..
and if lose or have travellers cheques stolen.....your cash is still safe and can be re-issued via a spanish bank quite quickly.....just follow rules and use safty deposit boxes ...
I went salou with my kids for years and thats what I did.....certain banks dont charge for your travellers cheques if you have certain accounts....ask bank if yours is one
have a lovely holiday and dont worry....things will be fine....brilliant place to take kids.....go the aqua park ...dolphin shows and a reptile zoo there as well as great water park all for the one price....better than the port adventura water park