When my step son was acused of touching my daughter can my ex husband can take my my daughter from me? we have 50/50 shared custody?

What are the ages of the two children (your step son and your daughter)? Assuming that your husband has placement of his step son, or visitation rights, I think it would be wise not to have the step son and your daughter together at the same time, at least until the investigation is completed to determine what, if anything happened between them. The answer to your question is yes; if the court has a concern that your daughter is at risk in your home because of the step son, the court would have the right to modify the placement schedule or restrict your placement with your daughter to periods of time and places where the child woould be protected and without the step son present.