Hi Helen,
I must just say I have found some of your posts very helpful especially the one about breast feeding. I am mum to two children a boy who is 5 and a girl who has just turned 4who was born with Downs Syndrome and I just recently found I the thank G-d I'm expecting twins early next year!
Re the car seat, it doesn't really matter if the children can't walk, at the end of the day if they are out growing the car seats that you carry in and out they need to be in a more secure seat. They can only go in when they can support themselves properly - ie sitting up. You can also buy car seats that have a double harness one in the normal place and one that sits across the chest giving more support whilst they are still smaller. Both my kids - even my daughter who has low muscle tone and is 'floppy' I put in a car seat like this when she out grew the other seat.
I hope that helps and anyway, also important, you need to take care of your back. They get bigger and heavier and you must look out for your back! I did my back in after my son was born purely from carrying the car seat in and out of the house!
Anyway, thank you again for your advice and hope you don't mind but would love to stay in touch with you over the coming months, need all the advice I can get!
Best regards and your kids look gorgeous!
Deborah