Ample is more than enough. Sufficient is just enough.
Children often read both words as 'enough' and move on. But one of them has room to spare and the other does not.
Ample means plenty, more than you need. If there is ample time before the bus, you can finish your toast and still find your coat without rushing. An ample picnic leaves leftovers for the ducks.
Sufficient means exactly enough to do the job. If there is sufficient milk for everyone's cereal, every bowl gets some, but nobody is having seconds. Sufficient is a careful, measured word; ample is a relaxed, generous one.
More than enough; plenty of room or plenty of something.
Similar: plentiful, abundant
As much as is needed; enough.
Similar: enough, adequate
Odd-one-out and closest-meaning questions can turn on amounts. A child who knows that ample means plenty and sufficient means just enough can separate them when both appear, and can tell whether a writer is describing comfort or a narrow escape.
Definitions and example sentences on this page are the ones a child sees inside Wordrealm, taken from our list of over 1,100 words. It is free to browse, with nothing to sign up for.
Plain-English guides to each test, from the councils’ own pages: Kent Test · Medway Test · Bucks Secondary Transfer Test