Not sure on the age of your children but there are several observational tools that could be used such as the CARE index (birth to 3 years) or the DPICS (3 years plus) - both are time consuming and costly though.
If you would rather use parent-report there is the Maternal Postnatal Attachment Scale (MPAS) or the Mother to Infant bonding scale - again child age restrictions apply.
There seem to be a number of options avaiable but it all depends on the age of the children and the method you would prefer to use.
We developed an instrument to assess the child's perception of parenting for 4-12 year olds. One dimension is 'Emotional Security' which is an analogue of perceived attachment. check out the instrument at www.scarf123.com which includes a video and a link to the peer-reviewed paper on reliability and validity. Angus Strachan, Ph.D.