Anywhere in portugal if you want a short flight but dont limit yourself. Took our 18 month old to canaries last month (flight time of 4.5) and it was fine.
Wherever you book though, try to get somewhere close to a beach. If yours is like mine all she wanted to do was run around which was a bit of a nightmare around the pool - neither me or the wife got much time on the sunbeds. At least on the beach you can find space to leave them off a bit and our little girl just spent most of the time playing with the sand