Good luck to you as well. I did read somewhere that you should ask a CM if you can go in with your little one if they have a fastpass and you don't. I think some people had luck with that.
As per our supervised children policy, if a child is under the age of 7, the child MUST be accompanied by a guest over the age of 14. Have the valid FastPass+ entitlement active for said child if you're only able to secure one and once the Cast Member at FP Return sees it is valid, tell them that he/she is under the age of 7. If a Cast Member tries to deny you access, immediately ask to speak to a leader (not a coordinator... a leader) as this violates one of our most important safety policies. This is a policy that we randomly get audited on during our many safety audits.