Ugh, how annoying… it's a shame they couldn't just let you plonk your toddler in a corner of the room with a phone/some toys and the occasional check-in from mum. I don't have kids, but unless they're running around causing havoc in the consulting room or screaming non-stop I can't see why that couldn't work for lung function tests? …people with children and no childcare still need healthcare sometimes, surely?
Anyway…at least they've managed to work out that their system is, in fact, slightly flexible, and given you an afternoon appointment. I hope it goes smoothly for you.
WRT peak flow meters, they can be useful, but you need to know what you're using it for, and get a good idea of what's normal for you.
Assuming it does turn out you have asthma, you can ask the nurse if it would be helpful for you to have one, and if so, how you can best use the peak flow meter as a tool to help you manage the condition.
The meters come with a chart, which gives you a general idea of what's a normal score for someone your sex, age, and height (with a note to one side that specifies how much lower than that you can blow and still be considered normal). But even healthy people vary a lot from individual to individual, so what tends to be more useful is to compare yourself against yourself, not against the chart.
For example, for my age, height and sex, the chart says that the normal value is 440 L/min. Coincidentally to this thread, I tested my peak flow this morning and it was 500 L/min. But even though that result is technically better than the chart predicts, for me that actually just confirmed my suspicions that my mild cold is affecting my breathing, because MY normal when I'm well is 550 L/min. A while back, I was consistently scoring only 480–500 L/min, and the nurse agreed that this meant I needed to go back on a steroid inhaler, because it's significantly worse than my normal result of 550L/min even though "normal" for a woman my age and height is 440 L/min by the chart.