Foster Care Support Group
Foster care is a system by which a certified, stand-in parent(s) cares for minor children or young peoples who have been removed from their birth parents or other custodial adults by state authority. Responsibility for the young person is assumed by the relevant governmental authority and a placement with another family found.
So in a way I've experienced some of this as grandma to them. The 3 of them take turns being extremely challenging and naughty. They came into our family with lots of baggage, as do all foster kids.
The important thing to remember is that all foster kids have experienced trauma of some type, but ALL of them have been abandoned by their birth parents, and that alone is a deep hurt that affects them in different ways. They act out, they're angry, they can't bond, they lie, they don't trust adults, etc.
We have to remember that they are children with undeveloped minds, who don't have all the skills they need to verbalize their emotions, who don't know how to process their trauma, who are deeply afraid of being rejected again. Our job is to love them as best we can, to help them develop coping skills, to give them grace for their emotions while at the same time teaching them appropriate behavior, and to find our own resources for coping (there are many support groups for foster/adopt families....ask your foster agency).
As far as the Down syndrome girl: you can't do much when out in public about how people baby her, but for anyone who is family or friends or teachers, you need to establish boundaries and teach them how to treat her. Most people have no experience being around a Down syndrome person and they don't know how to respond. They need education. Tell them what your daughter is capable of and what ways they can encourage her growth.
It's good for you to vent! My daughter vents to me regularly because she often feels at her wit's end with the 3 kids. It's not always enjoyable for me and my husband to be with them either, as they lie to us and have major attitude problems, but I keep reminding myself: love, grace, boundaries, compassion, consequences for bad behavior, and understanding that they are emotionally younger than their actual ages.
What gets us all through is lots of prayer! For them and ourselves. May God bless you for your willingness to care for these precious kids and may He supply you with all that you need to do so.