Even if you don't know much Gaelic it can be easy, with a little perseverance, to get into the habit of using a little Gaelic with your children, or with friends who are likewise learning Gaelic and willing to speak a little Gaelic with you. If you are not in the habit of speaking Gaelic it can feel a little strange at first to speak with your children in Gaelic but with time this strange feeling becomes lessened, and eventually it comes naturally. Speaking to your children in a second language (like Gaelic) is good brain-training both for you and for your children.
One of the easiest words to start with is the word "tiugainn" [IPA 'tʃukeɳ] which means "come" or "come on". You could also say "tiugainn leam" which means "come with me". The word "leam" literally means "with me" (it's a prepositional pronoun). "Trobhad" ['troət] is another useful word, which means "come!". For example "Trobhad an seo" ['troət ən ʃɒ] means "Come here".
The word "curamach" ['kurəmax] means "careful" and "bidh curamach" [bi 'kurəmax] means "be careful", a useful phrase to say to children in many situations. You can also say "bidh faiceallach" which literally means "be watchful". The phrase "na bidh gorach" [na bi 'gorax] means "don't be silly" and "bidh modhail" [bi 'moəl] means "behave".
A good word to introduce to very young children is "bainne" ['banjə], which means "milk". For instance, you might say to a baby or child "am bheil thu ag iarraidh bainne?" which literally means "are you desiring some milk?", or "am bheil thu ag iarraidh sugh?" which means "are you desiring some juice?". To a child you might say something like "am bheil thu ag iarraidh tuilleadh bainne?" which literally means "are you desiring more milk?", or you might say "am bheil thu ag iarraigh tuilleadh sugh ubhail?", which means "are you desiring more apple juice?".