The written word has power. Foster parents need to keep a record. The strongest material you can have in defending against allegations or advocating for your foster child is a well-documented daily journal.
You describe a very difficult time, especially for someone who has given so much to care for children in out-of-home care. I urge you to request a meeting or conference with the welfare department to address the allegations that have been made. Be sure to bring along a friend to support you, an attorney if you can afford one.