I use many assessment tools in looking at function and ability for children within my physio practice.
For pain we often use the faces or a VAS tool, as well as a picture of the body with colours and ask the kids to colour in their pain areas (if possible). i have occassionally used the flacc as well.
we often use the FEAS to assess relationships between parents and young children.
many of the standardised functional assessments are expensive to buy, which limits our access to these. and sometimes the standardisation doesnt quite fit the south african population.