I've been twice over the 'summer'. First time - bank holiday, utter disaster. Got there pretty much as it opened, but it was heaving, decided to go round the reserve as it was never likely to get any better. DD sulked and refused to look at the animals, needed a wee (hurray for spacious car, slow-moving traffic and portable potty) and eventually we took advantage of one of the unofficial shortcuts being offered by park staff to get disgruntled visitors out of the reserve.
Then we went to the amusement park, which was far more successful, so much so that I used the free return ticket to go back with a friend and her daughter (you can go back with the same number of paying visitors, and the exact same car) on a weekday. Plenty of rides that the girls could go on (they are both 3, but as the first height 'band' is 80 to 100cm the same should be true of your 2.4yo), including all the ones in the top left of the map (www.wmsp.co.uk/downloads/wmsp_parkmap.pdf) that are suitable ONLY for that height range, ie no adults. BTW the list of rides on the website is slightly out of date, the map is more accurate but of course doesn't give the height restrictions.
The thing you'll need to look out for with the rides at a non-peak time like you're talking about, they seem to cut their staffing by only opening the rides for a limited time during each hour. There will be an additional notice on the information sign for each ride saying that it will be open from 10 to 'til 10 past the hour, for example.
If there's any chance your 2.4yo will enjoy the rides, a wristband works out as a good buy. Both times I bought three tickets for myself, and didn't use all (I think I used one last time, to go on the carousel).
If your 2.4yo is potty trained, schedule a loo-stop before you go up to the top left corner, the walk back is interminable with a dancing toddler (loos are by the hippos).
I think that is all I have to divulge.