HELP with Gumboot Sizing for toddlers...

We are on our third pair of gumboots, I have to keep exchanging them for a bigger size at The Warehouse. We tried the Hi-hippo 18-24 months boots that velcro up the side first and to no avail, my boy has very thick/chubby ankles.

So I bought a size 4 in the rubber gumboots, still too small. Size 5 the same story. I can't even seem to get them on - is there some special technique in doing so?

I'm going to take them back tomorrow for a size 6 (ARGH) but just wondering for those of you with walkers/kids around the 12-18month mark - what size gumboot would they take?

This is totally doing my head in ......GRRRRRRRRRRRRRRR

Gremlins are in sz 5 too, I find it's easiest if I put their feet into them then make them stand up so their weight pushes their feet in properly.
Failing that, Maya had some very cool (but pricey) PP ones that had handles on them that made them easier to get on and off.

Josh is in size 6 ones. I found today that if I put them on him and then bent his legs so I could push his foot right in.

Awwww, he IS getting grown-up!  What a hunny. 

Ella's dad got her size 6 gumboots when she was only a year old, as she'd grown out of the ones that velcro up the side (thank goodness... they were cute but useless).  I thought he was crazy, but whaddaya know, though they looked a little big she still wandered about in them no worries, and we've not had to buy her new ones yet, despite her graduating from size 3 to 4 to 5 shoes in that time.