We took our DS to Lanzarote for his first holiday at 18 Months, flight wise he was fine, we flew mid afternoon going so held off his nap until the flight, he did get a little bit tetchy in the airport, but food and toys soon helped that, and it meant he slept pretty much the whole flight. We got him a straw cup for taking off and landing and as he didn't usually use one the novelty factor meant he drank out of it when we asked him to to stop ear popping, his dummy helped too.
Coming home it was a late evening flight, so I changed him into his pjs at the airport and again he slept most of the way home.
Take a bag of toys that your LO hasn't seen before, snacks etc and every so often pick one out to play with.
Destination wise, Lanzarote is lovely for families, we stayed in Costa teguise, it was October, but it was busy enough for an atmosphere, but in no way crowded, nice and flat to walk around and lots of choice in accommodation.
We have also been to caleta de fuste on fuertaventura (pre baby) this again was a nice resort, easy to navigate and family friendly.
Most areas of the canaries are family friendly, and fairly warm in March.