Hi Brian..Yeah,in theory you need a special work permit or a work visa..See links below.

http://immigration.gov.ph/index.php?...d=64&Itemid=43

http://immigration.gov.ph/index.php?...612&Itemid=103

I can work here legally because I applied for and got a 13a visa which is really a resident visa but if you are only going to stay for one year then I doubt its worth applying for it.
The good thing about a 13a is the fact that it is permanent and only a yearly report fee to pay (310.00 Pesos)..

I`ll be quite honest with you though.. I reckon you are going to have a pretty tough time securing any work unless you are prepared for a bit a salary decrease!!
I need a tiler to do my front portch area.. I think the Mrs has found a good one but he is a bit pricey at 400.00 Pesos a day!! You see my point? We used to spend more than that on a quick tea break in the building game back in UK.. Your permit is gonna cost you close to 7k which is about a months wages.
Obviously,I dont know your financial situation but If i were you I`d reconsider your plans and just plan to budget your savings till its time to get your family to Spain.. Your priority now is to keep the twins safe and secure..
Good luck with whatever you decide and welcome to the forum BTW!!!
Cheers,
Fred.