Not been on for a while...oops!!! 
Littlewhite I hate to say it but some convergent squints (turning in) dont appear until this age as thats when they really start to focus on things. The lens in your eye focuses from a very young age this is called accommodation, and when your eyes accommodate to look at things up close your eyes naturally converge. When children hit nursery they are suddenly doing alot more accommodating, and squints can become apparent. This means that your daughter might be longsighted and she should be assessed for glasses asap. Generally kids as young as your LO will be referred to your nearest eye clinic but this can be done by your optician.
martyrStewart squint surgery is either cosmetic, which will make the eye look straight OR functional to help some patients use the eyes together again. Your orthoptist/eye DR should be able to tell you which. If it is purely cosmetic it CAN get done at any age and its up to you.
damselindiss blinking can just be a phase that some kids go through. If you have a family history of squints or glasses it would be worth taking them to an optician.
wentshopping here in the UK (scotland) children get a eye test in their pre-school year at nursery (3.5 - 4.5) then there are no other official eye screenings. Its really up to you as a parent if you have concerns. Certainly would do no harm to get kids eyes checked when they are in primary 2/3 then before going into high school at approx age10/11.
Fanjo anytime she has them on will help towards preventing a lazy eye. It is quite a big difference between then eyes so the longer she can have them on the better. Do you see an orthoptist? Have they ever mentioned atropine as an alternative to patching??? You can pm me if you want more info....
Yanka I would get a second opinion tbh. We have attempted patching up to 10 yoa. If your child has a squint as well as the glasses this should be done with care. But if no squint, patching is always worth a go. Your visual pathway still has "plasticity" until the age of 9-11 ish!! DS 2, unless you have concerns wait till he's about 1 and ask to be referred to your local eye clinic.
THANKS FOR ALL YOUR INTEREST!!
WILL NOT LEAVE IT SO LONG NEXT TIME 