If the local authority agrees to place the youth under Section 20 Children`s Act 1989, the youth may be accommodated by friends or family members who work as nurses and may receive a care allowance from the local authority. It is clear in the case law that post-born agreements should be used sparingly and for short periods of time. Local authorities are cautioned that they are particularly cautious when receiving such agreements from mothers after birth, especially when there is no immediate danger to the child and where no provision is possible (Coventry Council/C e.a.  EWHC 2190 (Fam)). Parents have the right at any time to revoke their consent to an agreement in accordance with Section 20. If they do, the child must be immediately returned to the parents in accordance with Section 20 (8). It is very likely that LA will not be satisfied with its arguments in favour of the EPO or the IPO. I am only a parent as you are not a professional advisor, but the answer to your question is that all you have to do is contact the local authority and inform them that you want to take back the S20 you signed, then pick it up after contact or ask the social worker to take it home. I do not know their age, but it is quite possible that they were traumatized and emotionally rid of the distance, and it seems that there is no real reason to do so. I propose that an immediate return may, for the time being, be in their priority interest.
Heaven knows what they are suffering in care, and while it is possible, they will not feel free to tell you everything about it during contact. They are often too scared or forbidden to do so. If he is very young, they will not understand what is going on anyway like you. While the children are under an S20, sometimes instead of organizing support for you, if you need it and without a full and impartial investigation (including questioning and verification of domestic conditions, etc.), all they do is conduct a witch hunt and collect outrageous testimony from the evidence, intelligence of the police and so on for the sole purpose of making sure they get the order next time. And it is precisely in very young children that they interview them and collect false evidence by offering rewards or punishments. The A.A. cannot always have confidence in its impartiality and if it has already been obstructed by the court, you cannot be sure.