Never assume that a family will want you to give their child a bath as part of your responsibilities - each parent has a different mentality on what feels right as it relates to bathing.
To help navigate this scenario the first thing you can do is to ask this question in your intro call with parents or the morning of a job. Proper communication with parents will help you find out their preferences and understand what you're both comfortable with.
Some examples of when you may need to bathe or help a child change clothes is if you do a painting craft and it gets a little messy, you may have to give them a quick bath to clean them up. Or if you and the child play outside with water or do water activities, you may need to help change them into their swimsuit.
As a rule of thumb, children under the age of 5 will need assistance and supervision during bath time. Generally children over the age of 6 can bathe themselves and will require less supervision and minimal assistance.
If a bath is needed and ok with the parents, please follow these tips:
Make sure there are no distractions. Put your cell phone on vibrate and keep it with you in case the parents call or you need it for an emergency. Finish up any other tasks you're doing so you can give the bath your undivided attention.
If for some reason you need to leave the bathroom, you'll need to wrap the child in a towel and take them with you. Don't just take them out of the tub and leave them in the bathroom, as they could climb and fall back into the tub while you're gone.
Keep bath time short (especially for toddlers and infants). For toddlers or infants, bath time should be short and sweet. If their skin is starting to get wrinkly, they've been in too long.
Try to keep baths for younger kids under 10 or 15 minutes at most. That way, kids are less likely to get dry skin.
Check the water temperature before putting kids in the tub. Never just place a child into bathwater without checking the temperature first. Always start by filling a bath with lukewarm water, then slowly add warmer water to it until it reaches the right temperature (by testing with the inner side of your forearm).
If you are hesitant or unsure of what to do, always remember to reach out to the parents and/or your direct supervisor to ensure you have the support and direction that you need.