When Would a Court Grant a Change to Parenting Time

My question involves a child custody case from the State of: Colorado

My divorce was final 6 months ago. We have a parenting plan with a 50/50 split of parenting time. We have three children ages 9, 12, and 15 and I would like to receive more parenting time. Would the court consider changes based on these factors:

1. During dad's parenting time he took 9-year old son to orthodontist. Instead of staying with him during the appointment, he dropped him off to go run an errand. While gone, my son threw up due to the procedure being done and had to sit in the mess for 20 minutes while he waited for his dad to return.
2. 9-year old son gets frequent migraines (2 or 3 per week). Son came home from school on the bus to an empty house. Dad was supose to be there. He got a migraine while alone and had no way to take medication to make him feel better. He called my cell phone 20 times while I was in a meeting crying hysterically and begging me to come and help him. By the time I got the messages an hour later, dad had come home.
3. Fifteen year old daughter has missed 16 days of school in the last 4 months all while in the care of her dad. Her grades have dropped from As and Bs to mostly Cs.
4. Fifteen year old daughter was not allowed to hang around a certain group of kids. While I was out of town on a weekend vacation during dad's scheduled time he allowed her to go out with this group of friends and spend the night at one of the houses. Instead, she let herself into my house and had an all night party complete with drugs and alcohol and many other 15 and 16 year old kids. They trashed my house. Dad said I could come up with the punishment. I grounded her for 3 months and took away driving privledges. Two weeks into being grounded, dad said it was over and now lets her go out with same group of kids during his parenting time. He is doing this to get even with me because I started dating and he does not like it.
5. He does not make sure their homework gets done. The middle child is self-displined so this is not an issue, but the other 2 need a lot of guidenance to make sure it gets done.
6. He has allowed them to drop out of structured activities after school on his parenting days because he does not like it or does not care to push them to stay involved.

Dad does not abuse any substances, goes to work and pays the bills. Other then lack of displine and general common sense when it comes to the care of our kids I wonder if this is enough to ask the court to make changes.

I love my kids. I want then to have 2 parents in their life, but I also know the importance of displine and being there that he just does not get. He is one of twelve kids and he dropped out of school in the 10th grade (which he lied to me about) and he thinks it is OK for kids to do what they want and they do not need real structure or guideance. I want my kids to succeed, go to college, learn from displine and I think they learn the complete opposite when with him 50% of the time.

In relation to the 9-year-old... stuff happens. I would expect that Junior would have been just as sick had dad been at the dentist. You haven't told us why dad wasn't home when Junior arrived on the date of his migraine, indicated if we're talking about a one-time issue, or where your 16-year-old was when this was happening - the facts are relevant, so if you want us to comment you have to provide the context.

In relation to the 16-year-old... Why is your daughter skipping school? Is there something about dad's house that makes it easier for her to skip school than when she's with you? You can ground your daughter from certain friends; but you have your rules, dad can have his own. If your daughter chooses to lie to her father and break into your house and use drugs, it's like the skipping school issue - how is it dad's fault?

I don't know what the "structured activities" are, the significance of the kids "dropping out", or anything else relevant to that allegation.

Parents have different approaches to homework. Some parents are very strict, others tell the kids to do their homework and let their failure to get it done be a life lesson. We don't have enough context to comment on whether or not this is simply a different approach to parenting or something more serious.

Everything's rosy with the 12-year-old?

Agreed completely. Much of these things are parenting differences.