help with allergy testing

I have worked at an allergy/asthma practice for a few months. They have just started training me to do the allergy testing. Things seem to go well when I am testing an older child or an adult, but I have been having trouble getting the bubbles to appear when I'm doing the intradermal shots on a young child or an adult that has very loose skin. We do the IDs on the upper arms. I have watched the other nurses do it perfectly on very young kids, and I feel so frustrated that I'm not getting it right. I have practiced on the other nurses and do it fine on them. Any tips or advice would be greatly appreciated! I think I'd really like doing it if I felt more confident in my ID skills on children.
I would ask your colleagues to watch you do an ID on a child and see if they have any ideas. Are you going to deep, not deep enough etc. That would be hard to assess unless in person.

Well, they have watched me, and the problem is that I'm going too deep. They watched me yesterday, and I think the problem is that on looser skin, I'm pushing the needle down onto the skin before I insert it. On someone with firm skin, I guess I don't push down because the skin is already firm. I practiced on them yesterday, trying not to press down at all and just slide it across. I was able to do it that way, but I'm so nervous that I still won't be able to do it right on a child. The other problem is that I can only train when we have an extra person, so I'm not getting a lot of steady practice. I wish I could practice at home to get my confidence up. So, any tips or advice you could offer would be great!