What is the difference between UK and US curriculum? for Grade 1?

For Year1, the differences will be minor, it is only the later years where the different curricula come into conflict.

In general, the UK system takes a more holistic approach, teaching a little about everything at the same time, while the US system takes a more block-like approach, teaching on only one subject at a time. For example, in a US high school, they teach math in subjects algebra then geometry then trig then... while in a UK school they will teach some from each subject every year. My experience transferring from a US school at grade 8 to a UK school at year 9 (same 'year' just numbered differently) was that the UK curriculum was much easier. I cannot, however, see there being much time to develop these learning gaps after only one year.