why can't you leave out ler
you can, it is added
why can not I use "benim"???
Why not use aslında
aslinda = actually, gerçekten = really. I think there is a slight different meaning.
Couldn't it be passively?
Really my children changed a lot = My children really changed a lot. Therefore, Gercekden cocuklarim cok degistiler, should be accepted.
Not sure if that's good Turkish word order. But note that it should be Gerçekten.