hi, i can provide input on this too from my experience.
i would say the materials are completely irrelevant, let me explain why:
at this age toddlers love to scribble and sing and ask you how to say things and play in other types of ways. it’s super simple - you just work classics into that, without seeming to teach at all - just playing.
so scribbling, for latin my 2 year old scribbles all over my cambridge latin course (which is full of outline pictures, perfect for scribbling) and you can say “do you want to colour in pater?”, “let’s colour in mater” and soon they know all the vocab and you can say “which one’s pater” and they know. for grk i get outline pictures of grk gods and goddesses from the web (just google kids colouring greek myth or something like that and you’ll get lots of good examples), and print them, and write in big outline letters their names, and my daughter colours them in, including colouring within the ouline names (and so she associates the name with the pictures and learns the shape of the grk letters this way just while scribbling a thousand times over) - i got this idea from quintilian who said that kids a bit older should be taught to write by following their stylus through pre-written text in wax (i.e. they follow the grooves) - you can copy that with getting kids to colour in names that you write in outline.
i’ve been singing sappho’s first poem and reciting catullus to my daughter for bed-time songs. i started with dactylic hexameter but she far preferred hyndecasyllables since before she was 1 so i’ve stuck with that. massive repetition is what kids like, like reading kids storybooks a million times.
then for repetition i turn some of the basic expressions in the cambridge latin course into a game, like the rooms of the house (in atrio, in cubiculo, in culina). if you have toddlers, or spend time with them, you’ll know instinctively there’s a way that you can say “in cubiculo”, using reconstructed pronunciation, that makes them laugh (first and laugh syllables are long, middle three are short, and bi- is the highest pitch - if you say those 3 middle ones super fast, and maybe tickle them at the same time like at the end of the kids game incy wincy spider, kids find it hilarous for some reason). my 2-year old can now say which room of the house she’s in, say mater, pater etc., asks “how do you say X in latin” all the time, because it’s all a game…
i never sit down with a book and try to go through and teach it, and so, you see, for me the materials are completely irrelevant, there’s no reason to be limited to what publishers have come up with, you just create the games yourself - i do have though a long-term goal of following the cambridge latin course for latin (which for me is by far the best of all courses available), and so use the vocab and expressions from that (in atrio, in cubiculo etc. are all from that book).
lots of child language acquisition studies show that kids learn by listening to things even which they can’t understand yet, and so there’s no need to start from comprehensible input only.
so to summarise the above the 1st thing i’d say is that you should see what the toddler likes doing when they’re playing and just build in classics without ruining the game, it’s easy you’ll see.
the 2nd thing is that you need to be absolutely brimming over with enthusiasm and passion for classics. this has a contagious effect for everyone around you and particularly toddlers, who love being awed by things their parents like and copying. you need to make it seem like something they really want to be part of and they will then continue on their own initiative through questioning, pulling out books and just reading them (even if as toddlers they have no idea what it says) etc.
i’d be grateful if you let me know other tips you find! cheers, chad