My son is very attached to my helper even though she only joined us 2 months ago. So much so that when he wakes up in the morning, he wants her and cries if I try to hold him instead. It's quite distressing - why is he doing that and what can I do?

Is the helper the primary caregiver in your home? Are you a full time working mum? If so, it's natural that your baby is more attached to the helper. If the helper is good and you intend to keep her long term, I personally don't see any issue with it. :)