OK. First of all, I am saying that your children should not be asked to memorise these words as 'wholes', without any reference to relationship between the individual sounds in them and the letters which represent those sounds (the obvious exception is the word 'I'!). I am not saying that your children shouldn't remember them, just that they should go into memory through the sounding out and blending route, not by trying to remember the 'look' of the whole word as if it were a picture.
Why not? Because your children 'should' be learning their letter/sound correspondences and how to work out what any word 'says' that uses the correpondences they have learned so far. The way that they should work out what a word 'says' is by saying the sound for each letter (or group of letters, such as 'sh')from left to right, all through the word, then blending those sounds together to produce the word. This has to be practised until the recognition of the letter/sound correspondences is automatic and the process of sounding out and blending is so automatic that the brain can 'take over' and do it so quickly and automatically that the reader doesn't even know it's done it. They just see the word and say it...
Learning words as 'wholes', at best, interferes with the development of this automatic decoding and blending and 'may' affect the development of the left to right eye tracking needed for reading (this is not an automatic process, but is a learned one). At worst, it can thoroughly confuse children who don't know which strategy they are supposed to use when confronted with a 'new' word; do they sound it out and blend it or are they supposed to be able to tell what it is from its shape and appearance? Children frequently resort to guessing when faced with this confusion! Once guessing becomes a habit it is very difficult to eradicate (I know, that is my job in KS3).
Learning words as wholes has a bad effect on spelling (that should put you off, if nothing else does ) Apart from the lucky few children with photographic memories, many children who have learned words as 'wholes' can't remember the detail of the letter order within the words and, as they haven't been trained to pay close attention to the link between the sounds and the letters in the word they can often reproduce the letters of the word in completely the wrong order.
Teaching the unusual (i.e unusual for the child at that particular stage in their phonics instruction) letter/sound correspondence explicitly means that a) the child retains the necessary letters/sounds connections and b) they may well incidentally recognise the 'tricky' correspondence in other words (such as when you are sharing a book with them) and so effortlessly extend their reading vocabulary.
The High Frequency Words are No Big Deal. There is nothing intrinsically special or important about them. They are not difficult, most of them are perfectly easy to sound out and blend; they are just taught before the children have the phonic knowledge to attack them independently because it is believed that it is easier to write more realistic practice texts (i.e Readers) if some HFWs are included.
There is no advantage to teaching your child the whole lot all in one go; they should, if your child's teacher is half decent at phonics teaching, be introduced gradually as whatever programme they are using dictates. I'm not sure that they are even an assessment focus any more in EY/KS1.
If you google Letters and Sounds and download Phase 2 you will see how and when the govt guidance says they should be taught and introduced.
I hate them!!!