Well whenever I had playdates for my eldest child, with my 2nd child as a baby in tow... it was fine.
The other Moms there.... (they were my friends), ALL help.... with your other child too.
It was never any problem.
1) Get ready way AHEAD of time.
2) Make a LIST of things you need, if you have to, and check it off, before you leave the house. Make this list, the night, before.
3) Keep back ups of things, IN the car. Always. Clothing, diapers, wipes, bags, shoes, snacks.
Have a cooler in the car too... with blue-ice ice packs, to keep it cool. For snacks for your child.
4) ALWAYS, get ready, AHEAD of time, ahead of the time you think you actually have to leave.
5) AND... remember that, it takes at least 5-10 minutes, just to get the car loaded up with the kids AND their things... before you actually get in the car yourself, and start the car and leave, your garage.
SO, factor in that time, too.
6) and consider the time of day... and if there will be traffic.