Babysitting

Hey ladies! I’m a babysitter and I’ve been babysitting these two toddlers for a year and a half now. They are 2 & almost 4 years old. So my question is, how do I tell their parents that their children are way too old to be having a bottle? I’ve worked in 2 daycares prior to this job and the bottle was cut off at around 12-18 months. They act way younger than they actually are and are both still in diapers which is another issue. I understand that every child is different. But every time I get these boys to do something good to make their parents lives easier, the parents reverse everything that I do to help make life just a little bit easier for everyone all around. The kids only behave for me because they know that I don’t give in to everything that they want. But when their parents are around, they’re little devils and destroy everything in sight and the parents just watch and let them do whatever they want. How do I bring these things up without offending these parents?