Client groups?

The National Academy for Parenting Practitioners site refers to a "client group" - which is presumably we parents.

Here's the context: Acting as a national centre and source of advice on high-quality academic research evidence on parenting and parenting support, combined with practical knowledge of what works and has worked in different situations and with different client groups.

I thought the word 'client' indicated an element of choice, or option. However, according to my Oxford dictionary it means:

1. a person using the services of a lawyer, architect, social worker or other professional person.
2. a customer
3. Rom.Hist. a plebeian under the protection of a patrician
4. archaic a dependant or hanger-on.

Interestingly, its root is in the French verb cluere, which means "to hear or obey".

Ah, that makes sense then.

I haven't even got past the introduction yet.