My sister left her husband and kids in October last year, the boys were almost 3 and 2. Because there was no warning, the boys weren't prepared, and nothing was said. They've just accepted that they only see Mummy on the weekends. The only thing I've noticed is that they've gotten a little bit clingier with us, whoever their favourite for the day is can't leave the room or they'll cry or ask where we're going, but on the whole they've dealt with it very well.