The police are not reluctant to enforce trespassing laws... well depends upon what you expect them to do I guess.
Trespassing means being on your property without permission. So first, you have to tell them to leave. Then when they don't do it, you call the police. The police will then tell them to leave. Usually they leave at this point. If they don't leave, the police absolutely will make them leave and/or arrest them for trespassing.
That is what I expect the police to do, and they are not reluctant to do it. They are very familiar with trespassing laws and how to enforce them. Notice any businesses with "no loitering" signs? That's because teenagers like to hang out there for no reason, not buying anything, just because it's a convenient place to hang out. What happens if the kids don't leave when you ask? The owner calls the police for trespassing, the police will come make them leave. That's what they do. Happens all the time.
Now if you were expecting them to do anything more than that, yeah they are reluctant because there's not really much more they can do. If the person who is trespassing actually leaves when the police show up and repeat the request to leave, they can't arrest them.
What's important is not keeping the kid off your property every second of every day. What is important is having documentation showing that they have been removed repeatedly for trespassing or asked to leave repeatedly. Then when the kid breaks his leg, you have documentation showing they weren't allowed on your property in the first place, and thus you aren't liable for the medical bills because they were trespassing when the injury occurred.
Also, please don't give lawyers money unnecessarily. If you need a legal document drafted like an indemnification agreement, sure (though I would probably draft it myself, it doesn't have to be drafted by an attorney to be legally binding). If you need to sue someone or go to court, sure. If the lawyer is willing to give you advice for free (some are), sure. But I certainly would not pay a lawyer to ask about injunction procedures when I hadn't yet taken the first steps of (1) telling them they are not allowed on your property, and (2) repeatedly involving the police when they ignore your instructions so there is documentation to back up the position that their presence is not allowed. I am not a lawyer, but I live in California, and I think if I asked a California attorney about getting an injunction he would say what I've already said, you have to first establish that something is occurring in violation of your rights and the offender is repeatedly showing disregard of your attempts to enforce your rights.
Or, you know, you could just put up a fence.