Kids education

Time...that is what they need. Similar experience i had was with a lady who moved to my counttry from Australia. Her kids started to pick our local language after staying for about months. Once she bought tutorial books and the kid stay with us for most times. so allow your kids to stay with person proficient in english.

Hey Joy, firstly I hope you get the Visa with no issues. Regarding the language, both of your kids are less than 10 Y.O, which means they should not have any problems. Speaking of science , for ages under 15 learning a totally new language would  need a period of 1-4 months depending on IQ of an individual. To me, when I was in sixth grade I moved to Kuwait, and it took me couple of weeks to know Arabic without any previous background (even with accent!). All I did was playing football with other guys
For preparation, you can start showing them some English books or series such as National geographic for kids which is extremely helpful to get them to know the English. Don't worry about the accent, you'll get to know it easily.

Cheers