We had a very similar itinerary with our almost-4-year-old in March. We actually usually go at the end of February, but March worked better for various reasons this year.
We had a 4-day park pass with Park Hopper, and were there for a week. We did:
* Day 1 Hollywood Studios (he also loves Disney Jr & this was the perfect amount of time for this park)
* Day 2 Magic Kingdom
* Day 3 Animal Kingdom morning, Downtown Disney evening
* Day 4 Day off! Hotel pool & mini golf at Winter Summerland
* Day 5 Day off! Hotel pool & Downtown Disney
* Day 6 Magic Kingdom morning (did everything we missed out on on the first trip), Animal Kingdom afternoon
We decided to skip Epcot for this trip even though DH & I love it, and I stand by that decision.

We'll go when DS has more of an attention span for it.