I don't have any tips for re-capturing your roo. I'm really sorry about this situation.
If you don't already have them, a combination of cameras and BIG prominent signs announcing that you have cameras could be a good idea. I know that Ring cams can be programmed to sound a siren when they detect a person. This would also give you video/photographic evidence of his trespassing.
I'm a teacher and have worked with many children with many different disabilities. Even a child with really severe Down Syndrome can understand rules and boundaries. This is a tricky situation because things like having him arrested/charged could have really negative impacts for his future. And I'm not saying you're wrong at all to get the law involved, I just think it's an ethically tricky area. The above comments that the parents are really at fault are spot on.
If possible, and maybe with the help of a mediator (like a neighbor who gets along with you and this child's parents), perhaps you could have a conversation. If not, you could send a notarized letter. Either way, it could say: first, that you have suffered loss of your animals; second, that you are putting in place cameras to document what happens on your property; and third, that you will prosecute and or use civil court to recoup any losses. Include the amount you will be asking for each animal, and make those numbers LARGE. This should incentivize them to keep better watch over their child.
And while this is a bit more extreme: a child with a disability is being allowed to roam out of his parents' supervision, bringing him into situations (like going near your horses) that could result in injury or death. This is neglect, and it would be grounds for a call to child protective services in your area. This could actually be more effective than going the criminal route.
I guess my final thought is that you know your neighbors best. Things like criminal charges, a call to CPS, a letter, etc, can all be read as "aggressive" by some people.
Things like installing better locks on your cages, putting up cameras, etc, are more defensive. I'm a really non-confrontational person, so I tend to go much more in the defensive direction when protecting myself and my animals.
You should choose an approach based not only on what feels "fair" in the moment, but what is also least likely to lead you into a more intense situation.