I think if children are doing a fair amount of reading at home there is no need whatsoever to make them read books they hate.
The original ORT scheme was written to teach children the first 100 or so most common words with some tricky-to-decode letters. There is no reason why u cannot revise a few of those on a regular basis, but let your children read what they enjoy.
The main thing to remember is that children's reading improves through reading - no matter what books they read. I would not worry about levels in the slightest.
The most often used tricky words are the following.
In the first 100 most HF words, 40 are not entirely decodable:
the - he, be, we, me, she,
was, want, all, call, said,
of, to, one, come, do, down, into, look, now,
only, other, some, two,
could, you, your,
when, what, where, which, who, why,
there, were,
right, are, have, before, more.
In next 200, 55 are clearly tricky:
another, any, many, saw, water, small, laughed,
bear, great, head, ready,
ever, never, every, eyes,
find, friends, giant, I?ll, I?m, key, live, river,
people, pulled, put, thought, through, were, work, would,
coming, everyone, gone,
most, mother, oh, once,
grow, how, know, snow, town, window,
book, food, good, room, school, soon, too, took, door,
Mr Mrs
Another 13 are slightly so (partly depending on accent):
after, asked, can?t, fast, last, plants
animals, dragon, magic,
clothes, cold, old, told
Masha Bell