Children with Jansen's should be attending regular educational programs unless other diagnostic conditions interfere with their ability to learn. Children with short stature can be accommodated fairly easily in most schools with some simple adaptations.
A mobility device, such as a wheelchair, may be needed to move across longer distances. Ask if the child's teacher can move them in the halls in their wheelchair. The child may be able to walk within the classroom, with their wheelchair kept in the hall.
Class chair and desk
Often the classroom desk and chair may be too big. An easy way to make the chair more comfortable is to put a rectangle of foam, from 2" to 4" thick along the length and width of the chair back. I usually secure this by placing a regular pillow slip along the back of the chair from the top to the bottom. Then I gather the open end of the pillow slip, fold it upon itself, and use a few safety pins to close it under the bottom of the chair. Now that the child is sitting so that the knees are at the end of the chair, it is time to look at a footrest. The child will be more comfortable with their feet flat on a surface. Often there is a 4" or more distance to the floor. I often find a box about the width of the chair, and 4" or more high to make a footrest. I fill the box with cardboard, newspapers, foam packaging----anything which fills the box. Then I tape up the box with duct tape and put the box in front of the child's chair.
We usually accommodate one bathroom near the child's class. I place toilet safety frame bars on the toilet, and a large wide step stool in front of the toilet. We have begun using a 4" high plastic exercise step bench as the step stool. It can be mopped (custodian thanks you) and is wide enough to not create balancing fears by the child. The child uses the toilet bars to hold onto while stepping onto the step stool and also to hold on to while undressing and dressing. Boys may be able to use a hand held urinal as well. We also usually have a step stool (same as the toilet) at the sink. Since the soap dispenser is often out of reach, we use a small liquid soap dispenser on the sink. We have been able to accommodate most of our knob towel dispensers by a hanging dowel rod. I cut a 1/2" dowel rod about 12" long, drill a hole in the top, and attach the dowel to the back of the knob with a cable tie or string. The child then uses the dowel rod to pull the knob down and progress the paper. We've also used Kleenex hand towels on a low shelf when the above adaptation didn't work on the towel dispenser.
If the lunch table has built in seats, they may not work for the short statured child. We have set the child at the end of the table in their wheelchair. We have also used a separate chair which allowed the child to sit closer to the table. We've also been able to have the child sit on a regular seat with a small footstool under their feet to provide more support.
The PE classes easiest to adapt have been one in which the teacher gives all of the students a ball and lets every child practice the task against the wall or to one other child. We do use only soft textured balls with the boys (not a hard basketball), even if other peers are using a hard ball. The gym may be divided in 2 halves, with only soft balls on one side, and hard basketballs being shot at a basket on the other. Some of my students have their own exercise warm ups, which does not include running, jumping. Each class session, a different child joins the student to do "their" warm up program instead of the typical class warm up. All of the students seem to enjoy this. Sometimes (less than 25 % of the time) the student is removed from the regular PE class. They pick a peer who participates in an alternate activity such as Wii Fitness or Wii Balance games, cup stacking, or juggling with scarves.
Recess activities are very dependent on the setting and opportunities that other children have. If there is a playground structure, sometimes the child gets onto the structure and stays in one area interacting with their peers as they pass. We have had an activity "bag" with items such as ring toss, a ball on a string (so the child of small stature can retrieve it by pulling it in after it is thrown), beanbag toss, sidewalk chalk, etc. We have also had the child have a Power Wheels car available at recess for the child to drive around while friends run around.
Most of the accommodations made for the child for school are made so as not to limit its use to just one student, or prevent another student from using the accommodation. For instance, a majority of the students use the "dowel rod" stick to progress the paper towels---even if they can reach the knob. Other students often use the step stool to reach the sink. It helps them too. So don't hesitate to ask for accommodations and try to make it more than something your own student can benefit from.