OK, here's my take: You have choices.

An Intex up to 15 across can be as little as 30- 33 inches deep--your 3 year old should be able to stand in 30 inches of water, or less.

If get a ladder, the ladder comes out after swimming.

Intex makes VERY tight-fitting covers--a 3 year old MAY tear it, but will he climb on it? I don't know. A temporary fence may be appropriate.

Also, IMHO, a 3 year old should NEVER be in a yard unsupervised, especially if there's a pool there.

OTOH, if you get a standard AG pool, get one with a deck and fence. Plus, most places, code demands a self-closing gate that denies access to the ladder. It's not that hard to keep a pool safe.

But when I had my Intex, my older kid was already 5 and very reliable for a 5 year old, so he could be trusted not to go near the pool unsupervised.

My pool has a VERY tight fence and absolutely toddler-proof fence. No horizontals to climb on, 3.5" spaces between the pickets (4" is the max allowed), a gate with 1.75" spaces, a Magna-latch lock that the release is a foot above the gate-which, along with the fence is 4' high. My 2 year old isn't even tempted to try, it's so daunting. And he's been in it since he was 6 months old.