Does anyone feel their foster kids seem a bit stuck at a certain level of behaviour or manners?

I've had my 2 foster children for over 3 years and everyone says how much they've come on, how well they're doing etc and I do know that's true but in certain ways they seem to be stuck at the level they'd got to 3 years ago. Is that a 'thing' for looked after children? Do they find it hard to move on from the skills they had when they went into care?

Some examples of my kids off the top of my head:
They always kneel on the chair to eat at a table, despite me telling them every day for 3 years to get off their knees.
The eldest will still automatically put his fingers in his food despite frequently being reminded to use cutlery.
They both touch things in shops all the time even though I always remind them to look with their eyes not their hands.
A few mis pronunciations from 3 years ago are still in evidence - lep instead of let, bicsuit instead of biscuit, gived instead of gave etc.

It just seems to be that no matter how many times they're reminded they can't move on from what they learned with their birth family.

The things I've mentioned are pretty inconsequential but they just got me thinking, do fostered children get 'stuck' in certain ways at the point they were fostered?