There is a fine line. Practice this year began February 25th and goes through June 15th, which is the official day that OHSAA states the season is complete. As stated previously, 7th and 8th graders can not practice with HS age kids period...end of story. If they are "working out, conditioning" during this time period with the HS team they may be in violation, as OHSAA does not have this spelled out so clearly. Outside of these dates you would be ok as time outside the season is considered "Open Gyms" and anyone can participate according to OHSAA. I have seen many a JH kid playing basketball with HS age kids during open gyms outside the season, they just cant in season.
In years past I have seen JH or younger age kids being "managers" for the softball team, just like you do in football and even basketball....Those kids that are shagging fly balls or kicks, and returning them to the coach or player. Could even be a kid playing catch or receiving punts, all during the season. Is this considered practice??? I don't know if OHSAA considers it practice, but I don't. Even the one throwing soft toss from behind the screen I would consider to be ok, but OHSAA may not.
In closing, I believe we all know how a practice runs. All the girls participate from start to finish in all the drills and are working out together in a group. If you have one or two individuals that are just there shagging balls, doing some soft toss, I think you would be alright. Where you might get into trouble is when you have those same players throw with the team during warm-ups, then throw on catchers gear and warm up a pitcher, then go over to 1B and take throws from infielders and then finish off the day throwing BP from behind a screen. Use some common sense and you should be alright. IMHO...FWIW