Hi -
Sorry, wasn't on MN yesterday!
I was a primary school TA (male), and in things like PP children always wanted to use all the available effects, fading one slide into the next in lots of different ways, colour effects, text 'spinning' onto the page etc.
You can't really specify a font size, as it will partly depend on how the Presentation will be viewed (which DD may not know until 'the day', though, hopefully she might be able to find out beforehand.)
If it is being projected onto a screen, or interactive white board, so will be a large image, you don't need the font TOO big. If on the other hand, it's being viewed on a computer screen or on a lap-top, that the kids have to crowd round, then it needs to be larger. I don't think you said what Year group she is; obviously the older the child, the more sophisticated the wording and content needs to be.
Maybe plan it on paper first, like a 'storyboard' for a movie. So compose the captions, text, labels etc first. Quite often, Presentations are done with bullet points, rather than text like an essay; but a bullet point may need a few lines of explanation.
You will need different sizes for different things: for the Page Heading (largest); sub-headings, if there are any, (bit smaller); explanatory text, (smallest). Maybe just type a 'mock-up' in Word first, to see how it looks.
Probably best to use a BOLD font for a lot, if not all of it, as standard font is normally used on a printed page, so is thin and may not stand out enough on a slide. If coloured text is used, don't have too many colours, and tie it to the content of the pictures if you like; thus, Springtime could have green or yellow, Autumn obviously orange or brown.
We used to have a Presentation program at school (not PP) that had ready-made backgrounds, and one was an old fashioned blackboard, complete with wooden frame and ledge for the chalks. That looked super with bold WHITE text on the black background.
If you put coloured text on a coloured background, make sure the colours are suitable and still easily readable; you often see web sites with text that is too small, and unsuitable colours so it can be almost impossible to read it! Quite often you see similar effects in magazines, where designers get carried away and the text disappears into the background.
Using bullet points, you can make them come on-screen one after another, or all at once, whatever seems most appropriate.
You could probably type the text in Word first, then copy it into PP. Do you know the keyboard shortcuts? Ctrl + C=copy; Ctrl + X=cut (looks like scissors); Ctrl + V=paste (because it's the next key along.) Ctrl + Z is often 'undo', or 'delete' but can vary depending on machine. Ctrl + A is 'select all' usually.
And MOST IMPORTANT OF ALL: don't forget to Save regularly as you go along; so many people seem to think you only Save at the end. So, as soon as you add a new bit, Save it. Professionals keep different versions, so they have a choice of 'routes' as work progresses.
Good luck, enjoy it, and I hope it is successful.