I actually think this is the worse age. I have not really had any problems up until the last couple of months. As has been said, Ben really needs 18-24m but they are too long
I have tacked a couple of pairs so they stay turned up, otherwise he starts to look like a slug with his trousers trailing behind him
I am finding with Ben wahm made fleece trousers are brilliant and pretty cheap
and really the cheapest brands you can get seem to be the roomiest, we have some George jeans which are brill.
We do have 2 pairs of C4C but he is wearing 12-18m as they have been too big for him up until now! They are just becoming a nice fit.