Early in Level 2 challenge 1, the phrase is “do you want me to watch your children?” and the answer is “wyt ti’n moyn i fi gwylio eich plant chi?”, but if we’re using the polite “chi” for you in “your children”, why are we using the familiar “wyt ti” form at the beginning?
The “chi” is not only the singular polite form, but it is also used if you are talking to (or about!) multiple persons. So you are talking to one of the parents alone, using the familiar “ti”, but in “your kids” the your is plural (which in English is indistinguishable from the singular), so you use “eich … chi”.
Thanks Hendrik, just to clarify: does the plural belong to the children, or the (implied plural) parents? In other words, if I were asking you alone (Hendrik) about your two cats, but I was in the habit using informal ti with you, would I still say “eich cathod” as you have plural cats, or “dy gathod” as there’s only one Hendrik?
The latter – it’s “eich” whether it is one kid or more, as long as you are talking about the (plural) parents.
(Just be glad that you’re not learning German, as we actually have a distinct “familiar plural you” to maximize confusion )